After I retired my last smartphone, a Nokia something, the same thing happened. I used it purely as a mp3 player when walking the woods and it would randomly call the emergency line (not 911 in my country)

I barely could cancel the call before it went through as of course I was walking and had headphones in.

I figured it had something to do with a button... it got more annoying over time so what I did to fix it was: change the emergency number to my girlfriend`s