Ethiopians are black, but for Ethiopian Muslims, it makes sense that they identify with Islamic culture. Even though they are not ethnically Arabs, Islam is an extremely influential force in Arab culture, so devout Muslims that are not Arabs may still have more in common CULTURALLY and SPIRITUALLY than they do with other black people.
Also, if you are in America, there is a very big difference between African-Americans and African-Africans. Some Africans may not like the African-American culture or they want to hold onto their own cultural heritage. People who do this may SEEM to be disassociating themselves from black people, but in reality, African-American culture may be difficult for them to relate to.
Also, Africans in America with a strong Muslim foundation are not always accepted in America (well, Muslims in general are not always accepted in America).
I have met Africans in America from Nigeria and Senegal and they did not isolate themselves or feel superior however, they did have strong pride in their heritage and culture, so they stood out among other African-Americans...