pdd doesn't = idiot

We were at Bob's baseball game and two random boys from the other team were playing a DS.  They were about 6 or 7 years old.  SJ approaches the boys and tries to ask them a question about the game they are playing.  In my mind, I am so proud that he is attempting to make a connection with kids he has never seen before.  This makes me so happy, but then I hear the one little boy say something mean to SJ.  He said, "You already asked me that twice.  What are you an idiot?"  I stand there frozen.  Should I say something to the random boy or should I let it go?  It is not as if I could go up to the boys and say, "He has PDD.  He is not stupid."  Kids tend to call other kids idiots and not really think they are stupid.  SJ either didn't hear the boy or didn't care, because he continued to try to talk to the boys.  When I realized that they weren't interested, I called him over to sit with me.  I am still proud that SJ continues to try to make friends and I sincerely hope that no one ever calls that random little boy an idiot.  No one deserves that.