Dude is allowed to call his sexuality what he wants, but fantasizing about wanting a male dom who you bottom for anal to isn't straight.

I don't see how this isn't contradictory.

Oh I'm straight, lemme get donimated by this bear I've been fantasizing about, oh hey, I'm still straight by the way.

No.

If that dude tells people he is straight, he is lying, like a closeted person, who is either in denial or ashamed of his true nature.

If you're saying its ok for him to lie about it, to be closeted, to survive existing in a bigotted environment, thats one thing, but...

...its entirely another thing for him to ... actually think and believe that he is straight.

Thats delusional.

Words have to mean things, otherwise they are useless.