Looks staged but can see how it could easily happen maybe a little further down the road. Or has been mentioned with an item a little more noticable like paper on the rear window.
I never leave the car running though when exiting the car even to quickly take something out the boot. Too paranoid that the door will lock behind me (very unlikely to happen but am weird like that, hey I check my car is locked 2 times before walking away from the car and then a 3rd when walking away!)