My uncle is a 57 year old gay man......Has never been with a woman in his life but can appreciate a good titty.......He's even gone so far as to don a pair of fake boobs just because he enjoyed how he looked in them. He's not trans, he's not bi. He's just a gay man who likes tits.
Considering tits aren't even a sex organ, just a feminine part of the body sexualized by some, it's not necessarily something you can use to verify or deny someone's sexuality.