Most of the African Americans that Romney won probably live in rural areas.
That makes some sense, at least outside the South as the heavily African-American counties there voted massively for Obama. I would also add the affluent suburban ones, otherwise those with household incomes over $100,000 and reside in the wealthy neighborhoods or suburbs.
It is true many working class whites vote Democrat, but many are also in smaller urban centres as opposed to large metropolitan ones and likewise many respond the populist appeal of the GOP while this repels a lot of the African-Americans as many of the populists have racial overtones.