I wonder if this is like yelling fire in a crowded theater. They should keep him locked up a few days while they check him out. Young and stupid get youngsters killed all the time.
We can assume he didn’t have peaceful intentions. It sure looks like he was going to shoot up the place but the fireman with a gun took him by surprise, he couldn’t raise his rifle without being shot first and he knew he was stuck. Hopefully we will learn about his motives. The story will likely disappear because it looks like a shooting was prevented by a concealed carry licensee.