As long as he didn't lie on his permit application, I don't know if he could be sentenced for buying a gun after the state issues him a permit. A gun merchant definitely can't be sentenced for selling him one. Therefore, he did it legally. Case law may say something else, but that's how it appear to me.
No argument that there was some sort of error, but I think the state "legalized" the ownership of his guns when they made the error. It wasn't the intent of the law, but the practical results were the same. Calling him a legal gun owner isn't stretching the point.