Strange rule it would seem indeed, but what is racist about it is rather subjective. I am no purist but I find profanity laced rap playing loudly from passing cars offending enough. If I lived in the neighbourhood of that bar I may have the same concern. All rap of course is not so bad but some of it is with mother-fu#@er or somesuch in every second line. I love "black" music and I could listen to Satchmo, Ray Charles, or John Hurt all day but rap invades my space.
As for hip-hop I don't know what the problem is.