You are right that the group should have charge him, but not being violent people, being young also, they were hoping for a better outcome. Hindsight, especially when it can be assessed from afar, is 20/20.
For quite a while, people were told that in the event of a shooter, you should all gather in one room and hide. This strategy was found to be very inadequate. I believe most training now is: if you hear shots, everyone should run and scatter and get away in any way you can. And fight if you have to.
That's not bad advice.
But I'd like to see a little more emphasis on the fighting. As in: if you are in a room with the crazy guy with a gun, fighting should be a top priority. Waiting and hoping for a good outcome should not be a top priority.
But our current culture doesn't tell people that violence can lead to a good outcome. "Nothing was ever solved by violence". And so many people act like sheep rather than fight.