You have a good piece of forensic evidence, the undamaged prop. Get a good magnifying glass and closely examine the threads. If that prop popped off on ground impact, those threads will be visibly damaged. If they are in perfect shape, that prop definitely came off in mid air. That could be a secondary failure however, sudden motor stoppage likely being what ejected the prop.
Here is a picture of the prop. I can only see a sliver of plastic out of place. The lower threads appear fine.