Ethnic is a synonym for not white so you can't argue ethnic prejudice against white people either
I thought after I posted that trying to explain the difference between ethnicity, race, and nationality would already be a total non-starter. See the Mercury Prize thread for instance.
Regardless, they've permabanned the dude now, hopefully he's learned his lesson. Or he joins GAF where they tell him he was right all along, 'the left' are the real racists, and then provide a ton of bite-sized unsourced 'facts' to really settle the guy in to his new home. Top work, activists of reset!