It just makes no actual sense. Some racist guy thinking all blacks look alike is not a new stereotype, but thinking they all have James Brown style hair is not a stereotype I have ever heard of. Even the black women who do wear wigs tend to not usually have the James Brown style hair when they wear wigs or weaves or whatever.
The other implication seemed to be that it would have only been okay for a white male to insult another white males hair. To which okay, then we apply that to everyone. Sarah Silverman can now only make jokes about white females. Anything else is sexist or racist or both.