Yup, when younger we're REALLY slow learners for some things (not everything), and even if we do learn something really well, put us under a bit of pressure and all the filing on "what to do and how to behave really nicely" goes missing again.
Sending us home for it does absolutely nothing whatsoever other than lead us to think the world is a very very stressful, painful and unfair place that wants to disrupt our routine even more and make it even scarier for us.
The school should have had a cunning plan already in place - safe zone for him to be in to calm down, social story to work through what happened and re-explain why it is wrong, proper apology from him, take expert advice, work with child parent and expert to see if the plan for that child needs amending.
Removing them from a situation where they or the other child is unsafe is acceptable if it's done in a sensible and temporary way. A formal exclusion that teaches them nothing and makes them even more stressed out is counterproductive.
People don't realise how much a piece of work or an object means to us. For someone to try to rip up or damage our work, it's worse than if they'd tried to hit one of our relatives, to be honest. Even dh at his age will go into a complete shutdown and panic if one of his pages of his book gets damaged by someone - he just cannot cope with it at all, and he's a businessman! How are we expecting a child to cope? Clearly at our age we don't belt people with a ruler (not many of us do, tbh) but a young child may well react in a very extreme way because their priorities for what's important are absolutely not NT priorities.
So yes, he needs to learn that there is no violence allowed, but the school needs to make it very safe for him by ensuring no child is in a position to try to destroy his work. And if it does happen, he needs to learn safe coping strategies - including plenty of time to grieve and rage safely over the damage to his things.