They are actually very distinct. American blacks, the ones descended from slaves, are from West Africa. Somalia is in East Africa, right next to the Middle East and Egypt. Somalians and Ethiopians are generally more slender, and possibly a bit taller, although maybe their more slender frame just makes them look taller. American blacks have more circular faces, and Somalians have more oval faces. Probably because of intermarriage with Middle Easterners, their facial features have a more middle eastern look. In fact, some look very much like a middle easterner with dark makeup. Somali and Ethiopian women can be extraordinarily beautiful, and many of the black international models are Somalis or Ethiopian.
I dont know if it was preconceived because I saw the picture after I knew they were Somalian, but I could tell they were not ‘hood NYC blacks.