I went back to read the article again, and I see they say it may explain why “some” people may be more or less religious. Well, if by “some people” they are referring to those with an IQ of 70, then fine. But most people, if not all, of an average intelligence (or indeed those with an above average intelligence like Bryan) have surely given it a deeper thought (i.e. using their System 2).
Kahneman also referred to something he called “cognitive illusions”. Anyone of any IQ could be subject to experiencing an illusion, unless they learned to guard against it.
Also, individuals can experience delusions regardless of their IQ level, e.g., when taking certain psychoactive substances, or when in certain altered states of consciousness.
Then, too, there is the tendency of some highly intelligent persons, to construct a rationale for their belief system that makes it more impervious to change despite contrary evidence.