It may be true to some extent because Higher-IQ people have bigger egos as well. So despite all the evidence pointing to a supreme-being, a creator, an ultimate force governing the law of nature, they the egomaniacs think what they've acheived in their life is because they are so smart. All those atheist 7 agnostics out there, did you can not create a fly. Do you think you make babies with your semen or it is the God that makes the sperm and egg to convert to a baby? is the farmer who sows a seed makes the crops to grow or is it God that turn the seed into a plant?
So it is not higher-IQ, it is the Bigger ego that makes people to more likely to disbelieve in God. We all know, thatone may have a BIG ego without being intelligent.