A senior colleague was heard telling her subordinate in office that her bedroom is big but whenever the latter come over to her house, he would do what's done in the bedroom.

NB, the lady in question stays apart from her husband who's serving far away in the North Eastern part of the country.

Could she be possibly cracking a joke or serious with her statement?

There's peace in minding ur business...

It's real.
She's not joking at all, her statement could be likened to a Freudian slip.
90% of Nigerian married women have an uncanny ability to cheat.
Most of them are already doing it while the remainder are waiting for a little bit of freedom/laxity from their husbands in order to exploit their cheating tendencies

That’s quite an interesting choice of joke to make. She knows what she’s doing.