"I am the city of knowledge and Ali is the gate. Nobody comes to the city except through the gate" ~holy prophet (saws)

I read with dismay the comment of the above-
mentioned hadith on this webpage:
qa.sunnipath.comissue_view.asp?HD=7&ID=12049&CATE=1

After admitting that ahl sunna's scholars have different opinion on the hadith i.e some said its 'daeef (weak)' and other said its 'Hassan (sound)' according to different narrations; the web-page by Shaykh Faraz Rabbani however said:

" the meaning is sound for the holy prophet is the
source of all knowledge..."

He however erroneously add:
" The main gates to this knowledge are
the four righteous khalifas--for classical cities had four gates, one from each direction--of whom Sayyiduna Ali (Allah be pleased with him) is one."

I challenge:
Where does the holy prophet (saws) interpreted it like that? -That the gate included the first three khalifa(Abu bakar, Umar and Uthman)? NOWHERE for he (saws) did not say ...ALI IS ONE OF THE GATES!

If it is so as he claimed, then why was Umar exclaimed after he gave an erroneous judgement before Ali had to correct him:
"...had it not been for ALI, Umar would have perished?

It is a big lie that every 'classical cities' has four main entrance. Where does that comes from?
This is how 'these people' always try their best to
destroy golden saying of the prophet (saws) on his ahl al-bayt (a.s).