May want to hone up on baseball's unwritten rules 
... Best not to have a long memory when it comes to P and U relationship. If you don't the umpire won't and if the other coach knows it bothers your son, that will get around.
Your son should just talk with his coach and let it go. As in what did he think and how best to handle going forward. He may have his own reason for not reacting or will at least become more aware of what the other team is doing and handle it from there. Could also see what his C thought as one of their "jobs" is to have a good *game rapport* with the umpire (after all that is his protection). I've witnessed an unwritten rule being handled and all 3 involved (B, P, C) acting appropriately. Right after I go clean the plate and look at the catcher and ask - are we all done. I expect a "yes, sir" and we move on. So far, so good. 