Is it normal for a gay guy to not want to date a gay ftm trans

I'm not the one who got asked out by our ftm class mate but it was my boy friend who's gay, I'm the bi one.
She obviously got rejected by him because he's in a relationship with me. But he told me the real reason he doesn't want to date her is because she has a vagina.

She's currently transitioning to a male with hormones, but he keeps making comments about her transition. Like how it isn't gonna fool him, and keeps pointing out what she can't do/have things like a biological male. My boyfriend also heard from her female friends that gay guys on Tinder were either telling her off for posing as a guy or fetishising her for being trans. Think they were trying to make him feel guilty for rejecting her. But he's mine and it's annoying how they don't care!

Personally I don't really care what people do as long it's not hurting anyone else or hurting them selves. But that's the issue, are they hurting themselves? I'm still kinda confused if I should tell him off or not, like is he right? Or maybe it's his personal opinion? Or maybe he's going too far and being cruel. He hasn't said anything rude to her in person.

Just hard to see the right and wrong straight away, because when I ask questions about the trans community in history/politics class the support group shuts me down.