The obvious variable is the expressed self-identity of the person involved.
What exactly does it mean to be gay? I mean, for a lot of these kinds of questions you kinda just have to accept that people know their own minds, even if that's not at all confirmable by strictly outside observation.
It's right there in the difference between sex and gender, where sex is fairly straightforward and gender is more nuanced.
Nope, we've been over this a hundred times.
If someone said "I'm Gay" but they dated, married, were sexually attracted to, had sex with, fantasized, consumed pornography about, romantized about, etc only the opposite sex, nobody would be bigoted for questioning their gayness.
Gay has qualities you have to meet beyond pure self identity. It is NOT just a label people can slap on themselves and meet zero other criteria.
"Tee hee, lol what does it mean to be gay?" Please. Being gay means you are sexually attracted to the same sex, it's exactly 0% complicated.
Words mean things and this is not an evil or bigoted concept.
If you tell someone who eats meat they aren't a vegetarian you aren't "mis-fooding" them.
If you tell someone who writes, pitches, shoots, opens doors, and jerks off only with their right hand that they aren't left handed you aren't "mis-handing them."
If you tell a married man who can't call himself a bachelor you aren't "mis...errr martial statusing" him.
If you call a shape with 4 equal sides and 4 right angle corners a square and not a circle you aren't being bigoted.