I wonder if the windows were glass or perspex.
if glass, something hard may have hit them from the inside during the knockdown causing them to smash, or perhaps the window flexed more than the safety glass could tolerate casing them to shatter, and when they shatter they completely disappear.
Perspex, in good condition, say 10mm thick, typically would crack rather than shatter. Having replaced a few boat windows in my time, well prepared and stuck ms35 or similar sealant on windows, glass or perspex, holds extremely well and is very difficult to remove..
Such a sad outcome.