I had that happen on one of my emergency exit windows. The trailer was sitting in the parking lot at a body shop waiting to get repaired from a tire blowout and hadn't moved in more than a week, and they called and said they heard a pop and the glass falling but no one was near it to see what happened. At first I wondered if they had bumped into it with something, but my insurance agent said they get a fair number of claims from the tempered glass just shattering like that and it's due to stress in the glass.
They just added it to the claim with the other damage from the blowout, which was fine by me. The blowout was on the other side of the trailer so no reason it would have been related.