Saying that someone isn't "Asian enough," "Black enough," "Indian enough," "Hispanic enough", whatever enough is basically saying that they don't represent your idea of what the color of their skin means.
說別人「不夠像東方人」、「不夠像黑人」、「不夠像印地安人」、「不夠像西班牙人」、「不夠像任何東西」基本上就是在說他們不符合你對他們產生的刻板印象。