Yes it's confusing but homosexuality means being attracted by your same sex.
That's different than having something stimulating your prostatic gland from the ass hole.
In fact not all straight men who received a medical prostatic massage by a male doctor and ejaculated are gay or even liked it.
I find it perfectly normal although unusual that a straight man likes his girlfriend playing with his arse or putting objects in it: he's attracted by her tits, smooth body, feminine face, pussy instead than by man's features, perhaps he loves her too.
At the limit I can imagine someone taking a big cock up his ass but not fancying a man.
Just think to transsexuals' straight admirers/clients.
I'm homosexual, I like taking a cock up my ass, but I'm absolutely not attracted by transsexuals, trannies, feminine or just too camp gays whatsoever.