it is recommended to reply greeting in the same way or which is even greater than what they greet you with. the question now is, did the Islam has it mode of greeting or it doesn't. if it yes how? Yoruba will say eku aaro, eka san o e.t.c for greeting while kneeling and the elders will reply aajire bi if it is morning, then they will pray for the young or child if it happens to be the parent been greeted. this is the mode of greeting in Yoruba culture, ALLAH A'LAM but what I think is most preferable is too be conscious of Allah (s.w.t) in the varied aspect of what you uphold in mind, because the standing in prayer is with bending in such a way that you will be looking down to where you will put your forehead,and in every standing bending and prostrating we do all says Allahu Akbar meaning Allah is the greatest, I think we should be conscious of this as well. even there is an ayah that idkulul l-baba sujada( surootul baqarrah verse 58) Surah Al-Baqara, Verse 58:
وَإِذْ قُلْنَا ادْخُلُوا هَٰذِهِ الْقَرْيَةَ فَكُلُوا مِنْهَا حَيْثُ شِئْتُمْ رَغَدًا وَادْخُلُوا الْبَابَ سُجَّدًا وَقُولُوا حِطَّةٌ نَّغْفِرْ لَكُمْ خَطَايَاكُمْ وَسَنَزِيدُ الْمُحْسِنِين َ

And when We said: Enter this city, then eat from it a plenteous (food) wherever you wish, and enter the gate making obeisance, and say, forgiveness. We will forgive you your wrongs and give more to those who do good (to others).
(English - Shakir)

via iQuran, the word sujud is also used here and its clear that they don't prostrate but some how bow while moving in, so I think the question we should be forwarding is bending, kneeling applicable in other affairs apart from greeting, like taking a food on some ones hand while kneeling to be given to ones parent or elders, because all those ayat in which our beloved brother(albaqir) brought does not bring greeting in except the mutual respect between fatimoh(r.a.h)and his father(saaw) in which the Yoruba can never do( the parent will never stand up to welcome their children talkless of kneeling to welcome them but they only prefer sitting, lying down while the children stand or kneel to welcome or greet them- this is obvious differeces). Allahu a'alm. Asalam alaekum warahmatullah wabarakatuh

if its cleared that mua'dh didn't travel and come back and prostrate before the noble prophet(saaw) then about the ayah in suartul taubah you have pasted the tafasir on it referred to adi who say to the prophet that they do not worship their priest and lord: TAFSEER SURAH TAUBAH CONTINUES
The last time we stopped at ayah 30
AYAH 31
They (Jews and Christians) took their rabbis and their
monks to be their lords besides Allah (by obeying
them in things which they made lawful or unlawful
according to their own desires without being ordered
by Allah), and (they also took as their Lord) Messiah,
son of Maryam (Mary), while they (Jews and
Christians) were commanded [in the Taurat (Torah)
and the Injeel (Gospel)) to worship none but One Ilah
(God - Allah) La ilaha illa Huwa (none has the right to
be worshipped but He)[]. Praise and glory be to Him,
(far above is He) from having the partners they
associate (with Him)." (At-Tawbah 9:31)
Imam Ahmad, At-Tirmidhi and Ibn Jarir At-Tabari recorded a
Hadith via several chains of narration, from 'Adi bin Hatim
(RA), who became a Christian during the time of Jahiliyya.
When the call of the Messenger of Allah reached his area,
'Adi ran away to Ash-Sham, and his sister and several of his
people were captured. The Messenger of Allah freed his sister
and gave her gifts. So she went to her brother and
encouraged him to become Muslim and to go to the
Messenger of Allah. 'Adi, who was one of the chiefs of his
people (the tribe of Tai') and whose father, Hatim At-Ta’i,
was known for his generosity, went to Al-Madinah. When the
people announced his arrival, 'Adi went to the Messenger of
Allah wearing a silver cross around his neck. The Messenger
of Allah recited this Ayah; They took their rabbis and their
monks to be their lords besides Allah. 'Adi commented, "I
said, ‘They did not worship them.’" The Prophet said, ((Yes
they did. They (rabbis and monks) prohibited the allowed for
them (Christians and Jews) and allowed the prohibited, and
they obeyed them. This is how they worshiped them.)) … They
took their rabbis and their monks to be their lords besides
Allah… that the Christians and Jews obeyed their monks and
rabbis in whatever they allowed or prohibited for
them…" (Tafsir Ibn Kathir (Eng Abridged), First Edition: May
2000], Volume 4, pp. 409-410)
-one day the prophet (SAW) saw a Christian man called Adi
ibn Haatib
-he was invited by his sister, who was already Muslim, to
meet the prophet
-while he was walking towards the prophet, he saw he had a
cross on his neck
-so the prophet recited the ayah of 9:31
When he heard this from the prophet he said we do not
worship our rabbis
-the prophet asked him do not they make halal haram and
haram halal? the man said yes
-then the rasul (SAW) said this is how you worship them
This man had the honesty to admit it
-he was thinking worship is only when you make sajdah to a
piece of stone or wood
-or make dua to these, the prophet will now take him to the
different forms of worship

These people want to use this hadith that Mu‘adh (may Allah be pleased with him) prostrated to the prophet and the Prophet did not call him a Mushrik; they say prostration is ordinary sin and that was why the Prophet just corrected Mu‘adh (may Allah be pleased with him). Sheikh Rabee’ bn Haadee al-Madkhalee (hafidhahullaahu) declared this hadith has da’eef (weak). He said the hadith is weak by isnad (chain of narration) and matn (text). As for isnad: The hadith comes through the way of Qaasim bin A’uf as-Shaybaanee and scholars of hadiths decalred him as da’eef (a weak narrator). Their statements concerning him are: Yahya bn S’ad al-Qataanee – Da’eef Shu’bah – Da’eef Abu Haatim – Mudtaribul hadeeth Nasahee – Da’eef Ibn Hibban – Da’eef Imaam Dhahabee – Mukhtalif fee haalihi Then in another riwayah in Musnad Imaam Ahmad, there is Inqitaah (broken chain) between abee Dhabyaan and Mu’adh which rendered this hadith weak as well. As for matn: Sheikh said it was not established that Mu‘adh (may Allah be pleased with him) travelled to Shaam during the lifetime of the Prophet (Salla llaahu ‘alayhi wasallam). What was established was that he went to Shaam during the time of khilaafah of ‘Umar bn Khattab (radiyallaahu ‘anhu) and he died there as a result of sickness. Then Mu’adh only went to Yemen during the late lifetime of the Prophet (salla llaahu ‘alayhi wasallam) and the Prophet died while he was still there. He then came back during the khilaafah of Abubakr as- Sideeq (radiyallaahu ‘anhu). Then Mu‘adh (may Allah be pleased with him) was among the elders of sahabah and very knowledgeable among them that he could not be ignorant of this aspect of Sharee’ah.