This article in "Nature" is apparently the scientific source for your posting. "The tombs of ancient Egypt have yielded golden collars and ivory bracelets, but another treasure — human DNA — has proved elusive. Now, scientists have captured sweeping genomic information from Egyptian mummies. It reveals that mummies were closely related to ancient Middle Easterners, hinting that northern Africans might have different genetic roots from people south of the Sahara desert. " "The study, published on 30 May in Nature Communications1, includes data from 90 mummies buried between 1380 bc, during Egypt’s New Kingdom, and ad 425, in the Roman era. The findings show that the mummies’ closest kin were ancient farmers from a region that includes present-day Israel and Jordan. Modern Egyptians, by contrast, have inherited more of their DNA from central Africans." The DNA only goes back to 1380 BC so the possibility of an earlier greater sub Saharan percent cannot be ruled out but still the majority would have been Mideast peoples. You will, of course have the Jewish slavery period. Now, the question may be where the Ethiopian people came from if anywhere else.
Agriculture in that region started around Mesopotamia (currently Iraq) and spread. I could see ancient farmers heading south, finding the fertile Nile region, and deciding to settle there.