If you pick a black person and then pick a random victim, it's more likely the victim will be white than black, because there are more white people than black people.
Then why are there more murders committed by black people (against all sorts of victims) then would be accounted for by their percentage of the population? What is your point, exactly? Yes, there are more "white" people than "black" people in the general population. That's not what's being discussed. What's being discussed is the rate of crime coming out of specific demographics.