If you look at the very bottom of the last photo you can see the latch and spring are still intact. It sounds like since the hood wasn't fully closed it was most likely moving around while he was driving and the amount of movement, maybe on a bump, was enough for the latch to be freed of the catch causing the hood to fly up and off.
Or the placement of the latch and the part it catches on isn't aligned properly. I know mine is as I've pulled up on the hood without moving the latch out of the way fully and they stay engaged pretty solidly.