A straight guys enjoying gay porn would be a bit weird, because it wouldn't appeal to him, but he could be curious or something, this isn't something I like to remember, but I once saw the Tila Tequilla lesbian sex tape and I got off watching it, kind of weird, since it's only vagina and that weird lady, for a split second I thought about my sexuality, but I'm ok, I'm still gay, it's weird but I'd never want to change it.
No one likes (probably a bunch of weirdos) to watch disgusting videos, but people do, why? curiosity, that's probably why your bf watched gay porn, which isn't disgusting at all, I actually really like straight porn, and I'm ok with watching the vag, so why wouldn't a straight guy look at two big dicks for a few seconds, only to come to conclude how weird it is or how hot it makes him feel.