Okay, think of it like this. Pegging, you know what that is, right? Guy gets a girl to fuck him with a strap-on. You wouldn't call that being gay, but they both boil down to the same thing. Some guy gets a dick shaped object rammed up his ass, but they're two different things because of who's doing it.
Think of cuckolding and hotwifing like that, but with intention instead. Cucks get off on feeling inferior or humilated by their wife or the guy fucking her. Hotwifers basically have their own favorite personal pornstar they get to fuck after watching them in action.