I setlled this issue before and elsewhere, but old news keeps coming back like a bad penny. All of what I am about to tell you comes straight out of the rules for the 1960 Census.
IF, and ONLY IF, Obama Sr. was an American citizen would his classification be either NEGRO or BLACK. Since Obama Sr. was a British citizen, and a nonimmigrant from Kenya, the census taker would have checked, "Other," and filled in the blank whatever the person told them. They used the names of continents for other non-citizens, such as "South America," and "Central America." These are, in fact, examples cited in the 1960 Census instructions. so, it would not be a stretch for a non-citizen from one of the countries in Africa to say, "African."
HOWEVER, here's a possible reason why Obama Sr. would have said "African" instead of Kenyan. The Mau Mau uprising against the British, that lasted from 1952 to 1960. Kenya did not become an independent state until 1963.
Barack's grandfather supposedly was imprisioned and tortured for his suspected role in the uprising. This might have been a good time for Obama Sr. to "get out of Dodge," and go to the US.
This is a dan Rather fake but accurate
I setlled this issue before and elsewhere,
What was on the Birth Certificate in Hawaii Discussions about the Census are non sequiturs. OBTW welcome to FR yada yada; non sequitur; yada yada; non sequitur
and what the guidelines were used to fill in the entry for RACE.