I'm skeptical. I've met some of the smartest people on earth and some of them indeed called others stupid, and I personally believe rightly so. The statement is on the level of "there are no stupid questions", which is also a myth. I can't back this up with hard data but in my personal experience I've witnessed all combinations of {smart, stupid} people calling {smart, stupid} people {smart, stupid} without any strong tendency towards a particular combination.