The parents' reaction seemed completely strange. If I were the parents, I would have said what I said, which is "what do you mean?" in a non-confrontational manner, and hopefully the kid would explain "oh, it's because my friend wore a pink shirt and ate a mango too.." or whatever the reason was. Instead of telling the child they are doing something wrong when we (at least, I) didn't even unerstand what was going on!!