Intentions only matter for so much, though. When people try to "do something" that they are entirely unqualified to do, they often end up making things worse. I'm not sure why anyone would think it was a good idea for a 17 year old with no tactical or medical training to go into a highly dangerous situation entirely unnecessarily in order to play TACMEDIC. The kid may have wanted to help, but anyone with any judgment should have been able to predict that there was a high likelihood of things ending badly. He almost died, he ended up killing several people, and now he could potentially spend the rest of his life in prison. For what? A used car dealership that was already badly damaged and was owned by someone he didn't even know? Discretion is always the better part of valor.
All that said, it appears to me that the kid actually handled himself pretty well once the SHTF, and it's pretty clear to me that he only ever used force in self-defense. Hopefully he end up acquitted.