I can not say for sure, but I experienced something similar but different.  I was sitting in the car a couple of years ago waiting for the females to get done shopping at Wally World.  I like to watch people as they get in and out of their cars.  It was very quiet, and suddenly I jumped when the automatic locks engaged on the car I was sitting in.  I looked to see if my family was coming, and could see nobody around. 

I just have to assume someone else in the parking lot had locked their car, and it locked ours as well.  It was a long time before my family returned to the car.  When asked, nobody had even touched their lock fob.  Makes you realize your locked car is not as safe as you would like it to be.