Also, even if these were all built by Africans, plenty of these aren't castles to begin with. Just because a building is blocky, doesn't mean it's a castle. I know this one didn't specifically mention castles, but still. Also, I wonder if not mentioning castles was intentional goalpost shifting; is this a reaction to that other hilarious thread, still arguing the point?

Castles are a bad yardstick to use because they were in many ways a product of European weakness and not strength: lords and nobles started fortifying their homes after the fall of the Carolingian Empire. A fortified city or military stronghold could be a more impressive feat of engineering yet not be a castle because it existed to protect a community or an army and not a household.