type do not equal “criminal” behavior in the way most people think of it. Sounds like he hasn’t even been caught yet, so it’s nothing more than an accounting fix that will come with a fine and penalties.
If all of these insights here don’t persuade him, let him know that judges do not put people into jail for making accidental tax mistakes. Want to know why? Because you can’t pay back the fines and penalties if you’re in jail. It serves neither justice nor practical interests to put someone in jail for something like this.