I'm highly dubious of any research that equates "went to a top tier university" with "is highly intelligent" as its only metric. Especially one that also says "but outside America that's not true".
Could it be that people who come from backgrounds that value attending a top tier school as a status symbol also come from backgrounds that (can afford to?) pursue a biollionare-making career? And that in countries where the billionaire class do not value top tier schools so highly, fewer billionaires went to top tier schools.
Could it be that people who come from backgrounds that value attending a top tier school as a status symbol also come from backgrounds that (can afford to?) pursue a biollionare-making career? And that in countries where the billionaire class do not value top tier schools so highly, fewer billionaires went to top tier schools.
Could very easily be classic correlation.