Ok, so this happened today

[Rich W.]

Safety glass always breaks that way no matter where its impacted. Side to side, top to bottom, completely. You can use a center punch in the bottom corner of a car window and the entire thing will instantly spider web like that allowing you to sweep the glass away with the swipe of a hand (preferably gloved but the pieces aren't sharp) to make access into a vehicle.

I’m not aware of data on thermally caused safety glass breakage so I can’t comment on that. But I have broken many car windows and that is how they look when impacted in a bottom corned with a punch. It doesn't take much force if the object is small. Like a center punch, or a flying pebble. But maybe it was just under stress and finally gave up? I’ve never seen safety glass break on its own but I think its possible.

Here’s a link to a blog that discusses the possibility:

Can Auto Glass Spontaneously Shatter? 5 Things You Need to Know | Only 1 Auto Glass