Yes, of course it’s because of his race. Like it or not, many people just do that: they vote because the candidate shares a same religion, race, background, and so on... She is a Republican, but she is also Black. When she has to choose, sometimes she chooses her political leaning (which, according to her, often), but sometimes her race—especially in an important instance like last year.
Then she is “NOT” a real Conservative, one who votes for the Candidate who has the like-minded Ideologies.