Strange looks absolutely delighted as Rita starts talking. He knows a bit about what happened with 9S at the ball, as Strange and 9S had a conversation about it while Rita and the rest were stuck underground. 2B was there, the two of them talked, 9S learned about the fate of 2B and of his world, and 9S and Strange had a solid bonding session about how it really sucks to hallucinate your loved ones. All of this is to say that he has no idea what went on between 9S and Rita but if it makes her blush this much, Strange desperately wants to know what went on between 9S and Rita.

He lets her grab his shirt and yank him forward but that big, shithead smirk of a smile hasn't left Strange's face yet. Thank you Ringmaster, this gift is awesome. "What happened between you and 9S at the ball?"

It doesn't occur to him that the contract went both ways: if Rita wanted, she could make him spill the beans on something just as ridiculous and embarrassing. It also doesn't occur to him that he's heading on a one-way train to getting punched at the moment.