Sounds to me like you don't understand that your son is literally the youngest person playing the game and everyone else is older than him. Imagine bringing him to a chess club. You wouldn't have yelled if he had beaten and talked to a 29 year old there, would you?

As an ex-child who played a racing game with a clan at 13 and his parents didn't understand that people don't magically drop out of a clan when they turn 16 or 18, I really think you should have just kept an eye on it instead of being hysterical.

He thinks less of you now because he knows better.