When transgendered people start dating people of the opposite sex, does that make the person of the opposite sex gay if they didn't know of the change?

I hope I am: Understanding this correctly. In a situation in which the person is unaware of other individual's actual gender - the person is not making a conscious choice to date someone of that actual gender. In other words, if a man fully believed he was dating /sexually attracted to a woman (who actually a male) - that would not make the man a homosexual.