ETOPS
That it was removed from ETOPS schedules with the prior pressurization issues shows that the system at least filled some of the Swiss cheese holes.
if it was anywhere at FL39 instead of 16,000 feet the decompression would have been much more dramatic - probably sucking that kid out the hole that lost only his shirt. Lots of ‘lucky’ elements to this.
The fact that the FAA did a mass grounding points to it being a factory install issue - not an Alaska maintenance issue - such as troubleshooting the pressurization snag.