You might also think about some counseling. I know it's nothing yet, and he's probably just going through a stage, but you stated that his father had a reactive/aggressive nature and in order to stop that, you might start now....or at least soon.......And he might tell a counselor more about what is going on in his head too.....
My guess is, he is with kids who speak of their dad during the day, and he's not really able to tell them anything much about his since he doesn't have him on a daily basis..........talk to him about that.........in his terms that he can understand........be sure to always ask him what he learned at school today, how it was, etc......
When they grow up and move out, you always think about the "I'm busy right now, we'll talk later" conversations that never happened.......so take it from someone who knows......the house can wait, the laundry will still be there, and the kids can help cook, not be in the way.......so be sure to include him more.....I wish I had even tho I have 4 of them!
Good Luck, take care and I'm sure you'll do just fine.