I think there's also a (small) correlation between IQ the personality trait of "intellect", a sub-trait of openness that measures not so much how smart you are,

I think there's also a (small) correlation between IQ the personality trait of "intellect", a sub-trait of openness that measures not so much how smart you are, but rather how interested you are in intellectual pursuits. My guess is that people who score higher on "intellect" are more likely the kind of people who "take ideas seriously". That is, they tend to follow ideas to their logical conclusions.