Look, a Black person playing metal is statistically peculiar, but who's to say that's a valid reason not to like the band? Metal can easily become stagnant, so it's beneficial to be as inclusive as possible. And even if some cultural stereotypes are statistically validated, the fact that a Black man chooses to join a metal band is saying that he has broken away from the pressure to conform to the image that his own culture has reserved itself to as a means of distinguishing itself from White people.
In other words, a Black person playing metal is less likely to bring with him all the negative attitudes and whatnot so often associated with Black culture. Culture can have an impact on music, but race is irrelevant.