Black African vs kafir

Black African and kafir both are nouns.

Word	Noun	Adjective	Verb	Adverb
Black African	Yes	No	No	No
kafir	Yes	No	No	No

As nouns, kafir is a hyponym of Black African; that is, kafir is a word with a more specific, narrower meaning than Black African:

Other hyponyms of Black African include caffer, caffre, kaffir.

Black African (noun)	kafir (noun)
an African who is Black	an offensive and insulting term for any Black African