I'm thinking mal-functioning anti-ice system.
Oh yup, good point- gets might chilly in the air .which stresses things like glass, so,that could be it.
Most likely the window heat controller failed. This is not an unusual problem. The window is made of several layers, the outer most layer being glass, for scratch and abrasion resistance. The other layers are plastic, with thin wires between layers for thermal anti ice protection. Window heat controllers can fail to heat or overheat. Fail to heat at altitude causes an immediate temperature difference between 50 degrees below zero outside air and 70 degrees inside air. this sudden loss of heat can cause the window to shatter. A sudden overheat condition can cause the same damage.