https://en.m.wikipedia.org/wiki/Pumped_Up_Kicks

This wiki article quotes the writer as saying it’s designed not to condone violence but to get people talking about mental illness and the way kids are raised.

It also mentions that either the writer or one of the other band members had a sister who was a student at Columbine. The telephone game effect is probably where your students are getting their view (somewhere along the way the Columbine incident being part of the writer’s desire to have a dialogue about what is going wrong got twisted into a being a celebration of Columbine).