He didn't want to play the game because he didn't want to burn a pitcher.
That same thing happened to us a while back. A parent on another team just forgot to approve a player and the coach didn't catch it. They proved his age and we saw him on their gamechanger from another league so we said no problem. One of the other teams in another game though wouldn't allow it so he had to sit out. They won and fortunately for the kid they played us again, I think in the Championship. Don't remember if we won or not but I remember his name was Wyatt.
Some are in it for the boys. Some are not.
Edit-To add to that, some coaches and parents are shady as F. And rules are rules for a reason. If the roster rules were not generally enforced there would be complete chaos. I think every situation is unique and yours sounds innocent. The situation we were in was against a familiar team from our area. It might be different if it wasn't.
The trouble with quotes on the internet is that you never know if they are genuine. -- Abraham Lincoln.