The author of the piece had the following to say:
The IQ scores are from the General Social Survey as reported by The Inductivist. I already knew that this sort of correlation existed, it’s pretty unsurprising as I noted. The same pattern shows up if you use post-graduate eduation as the dependent variable. And I spot checked SAT scores by denomination, and again the association shows up. All that being said, the title was obviously tongue-in-cheek.