First, I want to say this: I have no idea whether his claim that Africans got a lower IQ score on the test in question is true or false. I hope it is false. There's a possible explanation that is totally in support of the Africans, EVEN if the claim was true. Here it is:

IQ tests are culturally biased. If the test asks "How do you use a teacup?" a British person will be likely to know the answer - a lot of them use teacups daily. Do Africans use teacups every day? Maybe they'll bomb on the teacup question because they drink their tea from bowls as with Japanese matcha tea, or from gourds as with yerba mate tea. If you ask them "Is a rattlesnake dangerous?" that question is irrelevant to them. They have boa constrictors, but not rattlesnakes.

There are tests that are designed to prevent these differences from influencing your score. They're called "culture fair tests". Nobody here has specified whether a culture fair test was used (I searched the page).