Yeah, I'd say that's out of line and I'd keep an eye out for more comments along those lines. If it were me though I'd wait before making an issue out of it. As it is, it's a good chance to ask your son "well, what did you think about that?" He's going to have people, kids, adults, people in authority, bring God and religion up sooner or later. I know I wouldn't have the energy to fight against all that. Better to prepare our kids to think about and answer those questions on their own.
We go to church and God is a topic in our house, but we've still encountred situations where kids at school and even teachers say something that I disagree with, and things that are not the message I want my kids to have. The most common one is a fundamentalist attitude that says other people go to hell. That's not what I believe or teach, but my kids encountered that one as early as kindergarten. So yeah, we had to talk about that, about 'how different people believe different things,' 'here is what I believe,' and 'what do you think?'
Best wishes.
