Second guessing his actions because the other kid has problems isn't fair to him. I know it sounds callous but just because someone else, child or adult, may not have full control over their actions or know what they're doing (the kid who was off his meds), doesn't mean we're supposed to allow them to hurt us. The standard is still the same...use the level of force necessary to protect yourself.I had a talk with him afterward about bringing down the level of force for other kids who are smaller or weaker or special. I can't say he did wrong, but in a self defense situation it's too easy to second guess after the fact what someone should have done. OTOH, he definitely needs real training to bring his skills under control.
Regarding the bolded part above, I think he did just fine, it doesn't sound like he was excessive with his use of force. I would tell him that you're glad he protected himself and make sure he understands that such things are only to be done if he is afraid that someone is going to hurt him. Don't make the mistake of coming down too hard on him or he might hesitate to act appropriately if there is ever a "next time." What is it about his actions that you feel was too excessive?
If someone is attacking you, the last thing you need to be worried about is "defending without hurting the bad guy."If someone came at me like Jerry did I'd know how to defend myself against it but likely it would be with maiming force, I have not yet learned the more subtle points deflecting attacks without harming the opponent.