Think about this the same way you might think of, say, someone who really enjoys doing their own makeup. That's something often associated both with someone being a woman AND with someone being a heterosexual woman, and yet, there are a lot of women, including heterosexual women, who don't enjoy that, and plenty of people who are neither heterosexual women nor even women at all but who do enjoy it.
In other word,s just because something is or has been culturally associated with a certain group doesn't mean that association is correct -- and whenever it's presented as exclusive to a certain group, it pretty much never is -- nor that someone who likes or takes part in, etc. that thing is a member of that group.
Perhaps even more to this specific point, being gay is primarily about someone feeling sexual and/or romantic attraction to people of their same gender. It's about hearts and minds, not assholes or what people do or don't want to do with them. (Pardon my French.)
Someone identifying as a man also usually is about a million or so things, and usually, again, has little to nothing to do with what they enjoy sexually when it comes to their bottoms.
In other words, this is primarily stereotype, and if you want to sort out your gender identity or sexual orientation, you're unlikely to figure those things out through this thing, or have this thing play much,if any, part in those. Make sense?