After all the phone calls and Twitter alerts and whirlybirds have subsided, it appears that what happened was this:
Some student at Ball State (but we don't know who) yelled the word "Gun!" on campus...
...and the entire northern half of the state collectively lost continence.
The highlight for me is the surreal film footage of cops with patrol carbines clearing what appears to be a large lobby or atrium with the balcony above teeming with kids peering over, grabbing footage with their phones: Delta House right upstairs from the Green Zone.
Splendid performance awards to all students, faculty, law enforcement, government, and media involved. I'm sure nobody took note of the massively disproportionate response for future reference.