Having done the hyperbaric chamber training previously I have a few observations that we were told during the course.
Many are using the term "explosive decompression". We were advised that this term is incorrect; if you have had an explosion then that is a totally different problem. The term used is "rapid decompression" (note the title of the training video in post #224). This is defined as a total loss of pressure in less than approx. 14 seconds. The time used in the definition is based on the length of time it takes for oxygenated blood to circulate around the body and return to the lungs for replenishment with oxygen.
Secondly, most O2 masks are set by default to diluter demand. If the masks are donned in an unpressurised aircraft at FL380 they will not provide sufficient O2 for the crew as there is insufficient partial pressure to breathe. The mask must be switched to the emergency setting (unless A320 has a different system) to provide ram air O2 to enable breathing. If this was not known or done by the crew then the mask would be of little use.
While useful consciousness at FL380 is 12-14 seconds these figures are based on being aclimatised at that altitude. In a rapid decompression that time can be reduced to as little as 4-5 seconds due to the effects of numerous physiological effects such as 'The bends'.
Not speculating on the cause, just observations on others' speculation.