It would feel very odd indeed to be fully clothed while Bay is not. So Mat does begin undressing, but pauses halfway through at her question. His waistcoat and shirt have been divested, but he's still in his trousers.

"Oh. I...don't really know."

Frowning thoughtfully, he considers it. How did he know? Had there ever been some moment where it became clear? Not that he can recall. He just...always liked what he liked.

"Guess when I started to be about the age that you start noticing people that way, I just always noticed lasses and fellows." He shrugs, realizing that answer is probably unhelpful to her. If she's asking, there's a reason. And it doesn't take a brilliant mind to assume what that reason is.

"To be honest I've never really given it much thought. Just always been how I've felt, that I haven't any preference. I liked the look of both, gave both a try, that was that."