Inferiority complex.
They feel sad that they descend from slaves so they claim people/civilizations that have nothing to do with their true heritage.
I think the reason why they claim those groups + Egypt is because they live in a cultural European country and those civilization had drastic effects on the European continent whether it be through vast knowledge (Egypt) conquering spain (Moors) or forming the bases of judeo-christian values (Jews).
There were wonderful civilization in West Africa but since it is of little importance to the Europeans we don't learn much about it. African Americans are essentially just dark skinned European, so it's obvious they would have the same biasness.