What they list are the heads of household - or, more specifically, the owners of the land on which the household resides, regardless of race. More often than not those listed are white, because whites owned most of the land, I agree. But, those listed are not "all" white. I have several black relatives on there, along with a minority of other Negro/Mulatto and Native landowners. You have to follow up with other census documents to identify the race of the individuals listed, if you aren't sure.