I don't know anything about those three counties, but I suspect that although they are Appalachian Counties, they have not been as culturally isolated over the years from the national political scene as Southwest Virginia has, and are more much accepting of a black candidate.
SWVA is a region of extremes, and unfortunately, like I said in my last post, its people are still living in JFK and Lyndon Johnson's time politically, but have never gotten past the Civil Rights laws that were shoved down their throats. I know that it is a big contradiction since it was JFK and LBJ that did the shoving, but again, that's just the way it is there.