Americans look nothing like Anime characters. With their big eyes, crazy colored hair, pale skin, and outrageous fashions.
Real Asians use circle lenses to make their eyes look bigger in cosplay (and rounder and more Caucasian), crazy colored hair isn't natural to anyone and I have never met someone paler than me, and I'm a purebred German Jew. Race shouldn't play a part in cosplay. And if that group had said "Africans who cosplay are racist" they'd have been backhanded by the blogosphere. Going after Caucasians is easy. The fact is, effort is the only thing that matters. With makeup, lenses, wigs, and a well made outfit anyone can look beautiful and in-character.
Besides, not all anime characters are Japanese. And most Asians don't look Japanese at all. If anything, grouping all Asians together is a bit racist.