Tempered glass can be a time bomb just waiting to go off. If done perfectly, it's a glass that is very strong (possibly to the point of being able to take bullets) in one direction but incredibly fragile in others.

But it can also get manufacturing defects that can make thermal expansion randomly trigger that extreme fragility. I had a tempered glass TV stand just spontaneously explode on me some years ago.

There was a bump involved, so it could have been purely working as intended but you hit it in an unlucky way, or maybe it was a combination of the two where it should have survived that hit but a defect caused it to shatter instead.