Maybe they were actually a highly intelligent person being forced into the role of a christian due to social standings, or pressure? While being an atheist won't get you lynched, stupid Christians are still less likely to trust you, therefor they can show their true views to ones smart enough to understand the message, while also making Christians happy.

P.S.: I'm not saying all christians are stupid, just the ones who go around saying shit like "Atheists are less trustworth than Felons" or "All Atheists should be in jail!".