Your son shouldn't be happier if you understand the explanation. He didn't do his job. While he didn't get charged with a run, he allowed an inherited run to score. That's how he's being evaluated as a relief pitcher. Will your son be happy with his earned run average given his coach who makes decisions on who pitches will be dissatisfied with his performance?
I recommend you remove your phone number from the post. Posting a phone number on a discussion board is about as safe as posting it on the wall of a public bathroom.
The OP didn't give enough information about the specific game situation for anyone to say that he didn't do his job. In one situation, he could have won the game. In another, he could have lost it. At the very least one would need to know how many outs there were. A reliever who enters a game with bases loaded and nobody out has usually had a decent outcome if only one run scores.