No, not necessarily the richer - I can spot a direct correlation between the quality of the education system and the IQ reported here. Finland, the country with maybe the best schools(not Universities, schools) in Europe is leading.
The first sentence of the linked post, well before the actual maps, is "Please note: Quality of education greatly influences IQ scores, i.e. a lower average IQ is more indicative of lower access to wide-scale quality education rather than innate intelligence (as demonstrated, for example, here). Also, testing conditions influence results; wealthier countries are more likely to be able to afford better testing conditions for participants."
(There's other wealth-related -- and, on a country-level, social-support-network related effects, too, as early childhood nutrition and other social-environment factors have an effect on IQ that, again, has been demonstrated on an individual level.)