We've broken two windshields over the years. One was hit by the ski handle as it was being tossed out to the skier (duh). But the other was while the boat was sitting on the trailer, driving thru a grocery store parking lot. That tempered glass shatters into a billion pieces if it gets bound up in any way.
Any chance your mirror is on that portion of the windshield? Sometimes the bracket can put some stress on the frame.
We had a patio table shatter this winter too. Sitting in our storage unit with the boat & a bunch of chairs. Temps got below 0 a few times. But otherwise nothing touching the table. Who knows why.