I wasn't even aware this short cut existed until one day I was driving along, listening to an audio book. The book pauses, and suddenly I'm getting connected on a phone call, it's 911. I stayed calm and explained it was an accidental dial (They hate it when you hang up in panic).
I found it was due to me sticking my phone in the cup holder, it was holding the power button down or some such, and the vibrations of the road caused the power button to get pressed and depressed a bunch of times and must have hit the short cut. I researched all of this when I got home and disabled that feature. There is no reality in which I have an actual emergency and remember the weird ass obscure physical button shortcut for 911.