The writer almost certainly doesn't listen to Rush's show and probably never heard the song.
Notice the mention of Rush's "critics?" That means the story was lifted from an anti-Rush blog. Modern "reporting" at its finest.
I guess the 'reporter' is too lazy, or more likely all too eager to beleive the propaganda feed about Rush. If one Googles 'Magic Negro', the original LA Times story is the 1st item in the returned search. But I suppose a good attack on Rush trumps real reporting for today's MSM.