The source of this factoid is musicthatmakesyoudumb, a site run by an American software developer.
His process was to, for each college, get the most popular artists according that college's student's Facebook profiles, and to correlate those against the average SAT score for that college.
This would be better boiled down as "People who go colleges with the lowest admission requirements are more likely to say they like Lil Wayne on their Facebook profile".
The research is not peer reviewed, and has not accounted for any confounding factors.