I'm not impressed with the methodology. This conclusion in particular is invalid based on many factors suggested by other posters already.
In addition, the results were compared to a previous unreleased study of a similar nature undertaken in 2006. The average IQ score of the individuals using the then current version of IE was significantly higher than the individuals using the current version of IE now, implying that a lot of people with higher IQ are moving away from IE to other browsers.