Yeah some people CAN be heterophobic
But most people really just make heterophobic jokes to cope with stuff like trauma or having been oppressed and harassed by straight homophobic and transphobic people.
I mean, my parents are super invalidating and they literally ban me from listening to any music that is LGBTQ friendly or whatever, so whenever my parents play their music and the songs are about straight romance or heterosexual relationships I saw "eww default people music"
And it's not even real heterophobia, I'm not invalidating or oppressing anyone by saying "eww straight music" ya know??