You are right to be upset, his father was really out of order!
No matter how much he loves his parents, there is no excuse for this kind of behaviour, and he should have had a word with his dad. He's being very unsupportive.
In the meantime, maybe just try to be the bigger person and be REALLY nice to his parents. No point making things worse by retaliating. However, if he continues to disregard bad comments about you, I'd really consider whether that relationship is worth it, frankly.