Speculation, but let's go with the kid's explanation. He brought the gun to school to keep his classmates safe.
Plausible train of thought:
"26 people died because a gun man shot them at school" >>> why didn't anybody stop him? >>> "He had guns. All they could do was hide as quickly as possible" >>> so if somebody else had a gun, they could have stopped him from killing all those kids? >>> "I suppose that's possible." >>> *I don't want people at school to die, so I'm going to take protection*
The kid is 11. Even if he's been given proper training and knows how to handle a gun safely, he's still just 11. There's still a level of irrationality involved there that lends to making bad choices. That's why we don't let 11 year olds drink, drive, vote, operate heavy machinery, or live independently of their parents.
The kid screwed up. The parents probably screwed up to. But I don't think he was dumb, and I don't think we can conclude that the parents did NOTHING to educate the kid on gun safety. I think there's strong evidence to say they didn't do enough, particularly if the claim from the other student proves true.