Maybe so, but the question is: How did the voters know he was black?
If you can't answer that, you should be baffled too.
He did say he campaigned, went around and talked to people. Clearly there was SOME awareness of who he is. If he motivated enough folks in the black community, considering the demographics, it’s not surprising at all. The other guy probably thought he was a walk-in. Besides, there aren’t a lot of white guys named Alvin. As soon as I heard the name “Alvin Greene” I figured, “Ah. Black.”