All of this means that, very broadly, Africans are more genetically diverse than any other 'race'. You are almost certainly more closely related to a Chinese person, an Indian person, and a Navajo person than a random Senegalese man is related to a random Ethiopian. There is no genetic African group for intelligence to correlate with.
"But", you might say, "so many Sub-Saharan African countries have low average IQs. How can that be coincidence?" Well, it isn't a coincidence, and the fact that so many African countries have such low average IQs is PROOF that these low scores are not genetic in origin. These countries share social and environmental conditions, including poverty, colonial history, unfamiliarity with standardized testing, etc.
The one thing they do not share is exactly the thing the alt-right says predicts intelligence: genetics. These African countries are vastly genetically different from one another. If genetic group (or 'race') predicted IQ, we'd expect to see variation between the many very different genetic groups in Africa, while China, the US, India, and Bolivia would all be at about the same average IQ. That is decidedly not the case. It turns out that IQ scores around the world correlate with environmental factors and not genetic group!