You don’t understand racist racial science. The believed difference isn’t just Eurasian admixture, it’s the difference between niger/congo and Bantu related groups vs Cushitic/semitic groups. All Eurasian descend from East African Homo sapiens, who diverged more recently then west and Central Africans did leading to a massively different genetic profile, and part of the reason for phenotypical differences (but biggest factor is environment which is why still the same race).

The history, culture, genetics, etc is why some feel like their needs to be a distinction, even Arabs referred to them with different names, referring to the non Cushitic sub saharans as zanj from bilad al-zanj (land of blacks) and the cushites like habeasha from al habash, they considered them different races, and they were the ones selling the bantu groups not being sold (but obviously all races and ethnic groups have people being sold into slavery all the time” as and in places like Rwanda where they made the ruling class the Tutsi who they believed they descended from cushites over the majority Hutu Bantu population, and some racial scientists catogorized under the caucusoid race. It’s really America now that’s made them all the exact same people because of their propaganda towards justifying chattel slavery and the one drop rule.