Condolences to Mike and his family. What a horrible thing to happen.
But.......most treadmill safety lanyards are meant to pop the key loose as an emergency precaution for just these, and similar, reasons (we have one here at the lodge, and that key is everything). I'm trying to figure out how the girl got tangled up in it without it pulling out (DISCLAIMER: I didn't read the article, so I'm not up to speed on the circumstances).
My son and I were trying to figure out the same thing. The cord is supposed to fall off. We figure maybe she was playing with it and put it around her neck and maybe the machine started (on purpose or by accident if she put her hand up on the console while struggling). She might not have been able to keep up w/the machine, fell or almost fell, with the cord around her neck and was hanged.
Sad, whatever way it happened.