Can you elaborate? I think that I might understand what you're saying, but I'm not sure. Are you saying that UCLA math professors would be considered to be exceptional mathematicians but not exceptionally intelligent?

I think what Tao means is something like: among the total population of those intelligent enough to eventually become senior faculty at a UCLA-level department, variables other than intelligence are much better predictors of (the binary variable of) whether a given individual achieves (at least) that level of status (as opposed to, say, the level of more typical state universities).

This is not inconsistent with intelligence being the best predictor of Tao-like status conditional upon UCLA-level status. In terms of intelligence, ordinary universities might contain a large percentage of could-have-been-UCLA's even if UCLA-level places contain only a small number of could-have-been-Tao's.

I also suspect you and Tao (or at least, his public "voice" as reflected in his writings) may disagree somewhat about the relative contribution to mathematics of Tao-level and merely-UCLA-level mathematicians.