Over time, perhaps a couple of decades, the tension on the plexiglass combined with the flexing during pressurization in exactly the right manner to cause the windscreen to fail.
Hmm so lets see no NTSB report of what after all amounts to a very serious failure, no incident report to enable others to be aware of the problem, no AD to give ntoice to other engineers that the aircraft could have a serious issue. Infact it would seem nothing to avert perhaps another crew killing themselves and their passengers when suffering the same failure at FL285. Notwithstanding the FAA saw fit to review the incident and commend the crew.
It is a great story however.