I think what he was getting at was that they're not necessarily unintelligent, but undereducated. Africa isn't very rich a continent, and it takes money to build and supply schools.
I don't think that's what he meant, I think he meant that they've evolved in a different region and have abilities suited to that region and that inteligence is a lower priority (as far as evoulution is conserned)for them because of that.
stereotype:a stardardized mental picture that is held in common by members of a group and that represents an
oversimplified opinion, emotional attitude, or uncritican judgement
in other words, something that is generally believed to be true, in otherwords, potentially based on truth.