"You ain't so smart. I been believing in nothing ever since I was born" (O'Connor 194).
Here in this quote, O'Connor soundly debukes the myth that only intellectuals cannot believe. All the only thing a person needs to not believe in God is a closed heart. Isn't it funny that a simple country boy had more unbelief than the the supposed hardcore atheist Hulga?
You're right. You would think that the simple country boy would have more belief in God and O'Connor made his character seem that way. However, in the end, we see that Hulga defiantly had some belief in God, even if she was repressing it earlier in the story. That is more genuine than the boy who claimed to believe in God and turned out to be a creep.