Sure, you could argue forever what should be included, what's significant enough (only still existing buildings or also ruins? how well-known does it have to be?), if only historical castles should be included or also things like Hearst Castle in California (which is actually a large mansion built in historical style, with the main building looking like a church - if that's included, you could also include, say, Mar-a-Lago?).
It is also important in context to include castles in Africa to show that the area did contain castles. This fact often surprises people that Africa has castles and some of them dating back to the 11 century.
For example just by looking from my eye you are missing Lamu Castle https://en.wikipedia.org/wiki/Lamu_Fort Siyu Fort https://en.wikipedia.org/wiki/Siyu Thimlich Ohingahttps://en.wikipedia.org/wiki/Thimlich_Ohinga
And then in Tanzania you have the Gerezani Fort in Kilwa Kisiwani, the Old Fort of Zanzibar, the German Fort in Bagamoyo. And then Taleh Fort in Somalia.
I have not even started on either Mozambique, or Angola.