I suspect they are? I mean, if they weren't showing up then the restaurant would be out of business, no?
It does read a bit xenophobic, but it might be a pressure thing more than a nationality thing. People try to put pressure on those establishments. Sometimes, it's the chefs themselves who put the pressure on, sometimes it is visitors.
People have committed suicide due to the pressures involved in trying to get onto the list and to maintain, or increase, their stars. Failure is difficult and may even result in financial ruin, as if restaurants weren't already inherently risky.
So, I'm not sure that it is so much xenophobic as it is simply not wishing to be so publicly judged and/or pressured.