I don't think he was homophobic. His father was more scared of how his son would be treated by society than him being gay. I feel like his father went through something the same maybe that's why he became the way he is.
I hope that we will get more info about his father's past to see if it's true or not.
Yeah he’s not homophobic at all. He regrets his life because of hardships he faced and he doesn’t want his son to be in hardship and grow up to be a regretful old man like he is. It’s actually just him projecting his own insecurities out onto his son rather than him actively hating on gay people. He even said it “I’m just worried”. I think he really loves his son and doesn’t actually care that he’s gay but it came out really really wrong.

Finally a homophobic character! Listen I love the supporting friends and family but like.. this is still set in real Japan yk, no one opposing the relationship was weirder lol although id have preferred it was any other character instead of the absent father