I don't want to tell my boyfriend he can't talk about his job but....

My boyfriend used to be a college professor and he quit his job to be at GED teacher at both the men and women's prison. My dad who is staying with us for a bit doesn't like that. My dad used to work in law enforcement and he has asked my boyfriend why he doesn't become a GED teacher for actual law abiding citizens. My boyfriend said there are tons of resources for that but getting a GED program in a prison can be difficult. My boyfriend is extremely proud because out of the 27 total(both men and women inmates) 24 passed their GED test. He's so proud and I would feel guilty telling him he can't talk about this accomplishment in his own home but it makes my dad uncomfortable. Should I ask my boyfriend just to not talk about it and respect my dad or tell my dad that this is our house. I just don't want tension.