Yes. Full stop.

If you feel you're straight but find there's this one guy who's really hot and that gets you off, then you're straight. Your orientation is what you decide it is, and nobody else's to gainsay. There is even an entire subcategory of straight "MSM" (men who have sex with men).

The same goes for anybody else - if you aren't guy #1 and are questioning someone else's identity, then even if you find it odd or uncomfortable please just accept it and move on. They know themselves from the inside, in a way you never can.

Might they decide in the future to identify another way? Are they going through a self-discovery process? Working through internalized homophobia? Maybe. Maybe not. Not your circus, not your monkeys.