It would be interesting to know whether the alleged finding (assuming it holds up, which is always uncertain for this sort of thing) looks different in places where very smart people are easier to find, or for populations with more effective ways of finding very intelligent friends.

(For instance, I live near a city with a world-class university and a pretty vigorous tech industry in the area that encourages smart people to stay around. There's a pretty good supply of highly intelligent potential friends around here.)