I have seen this in a number of contexts and on a number of occasions both within my work with the public and in society generally in everyday situations, and as you say totally unfounded. I personally think it is this kind of use of ethnicity that frustrates some people and encourages negativity. I certainly would like to drop the word minority from some ethnic groups, as it is just not the case in my area, and conjours an image of victim, which then some decide to use. I also think we walk on eggshells around rude ethnic minority people for fear of being branded a racist, and allowances are made that would not be for rude people from a group with less power.