While not all practitioners of the Jewish religion are ethnically Jews (Ashkenazim, Sephardim, etc.) and vice versa, there's certainly a very strong correlation

While not all practitioners of the Jewish religion are ethnically Jews (Ashkenazim, Sephardim, etc.) and vice versa, there's certainly a very strong correlation. That's certainly enough to produce an apparent religious-IQ linkage, if indeed there's a ethnic-IQ linkage. (It doesn't, of course, say anything about causation.) You could similarly link the Hindu religion to dark hair, or other genetic traits common among ethnic groups who have a high percentage of Hindu practitioners. It wouldn't be true all the time, but it would probably show a significant correlation.