It would seem odd if it was a controlled descent to below MSA.
I suspect it may have started simply, as a controlled decent to an altitude where the air was breathable.
Instead of explosive decompression, it may have been a failure or partial failure to pressurise on the way up to FL380. If both pilots were already starting to suffer the effects of hypoxia before the TOC it may explain the 'gut reaction' to just get down rather than point the aircraft somewhere other than a fast approaching mountain range.
