He wasn't. He was in a building on campus that houses the YOUTH RADIO program where he WORKED. Yea, I've seen that referenced, but if that's the case, what's the whole deal about 3mi from home to school on a bike about ?
It's all bullsh!t, imho, and it appears that the worms are gettin' outta the can.
My guess is that he went home AFTER the LIVE SHOOTER DRILL they had that morning. He was probably working on editing the footage when he got a call, so he went back to the studio, in disbelief that this was REAL and not another DRILL.