The way he said all that was fine but the reasoning was awful. He basically said stay away from her because you don't take school seriously. OK I get that school's important but tf does that have to do with being friends? And heck he even said that he's trying to take school more seriously so that reason is nullified.
I don't mind the fact that the dad doesn't agree, that's fine. But at least give him a better reason for not agreeing.