I'd agree that this isn't a very convincing argument. There are some obvious reasons why people would be less finicky about authenticity of fiction on NK, considering that it's pretty much a mystery to most people. On the other hand American Southern racial issues has to be one of the touchiest subjects around. I can't imagine what the response would be if a white person had wrote, say, any of Toni Morrison's books. I'm sure it would get a lot of flak.

The author does hit some truth though;

People of color, on the other hand, are expected to speak only for themselves.

There was, for instance, the argument at Sundance over how a group of Asian actors should be portraying themselves in which Ebert rebutted:

And what I find very offensive and condescending about your statement, is nobody would say to a bunch of white filmmakers, "How could you do this to your people?" This film has the right to be about these people and Asian American characters have the right to be whoever the hell they want to be. They do not have to "represent" their people.

I feel like the attitude he's arguing against still persists, although that's not quite what the article is presenting.