training wheels, if I read your intent correctly, you are addressing the potential of a bad timing event wherein after the Captain headed to the loo, a decompression event, or a perceived one, arose that the CP felt he had to handle. And, sadly, didn't handle it too well. (Or perhaps another kind of malfunction?)
A thought to go along with this: above 25K, but not on O2 while the Captain was away.
Am I following you well enough?
FDR data might provide some insight as to whether this line of inquiry has some data points that align ... so those who are voicing frustration with all of this public discussion with no FDR data known to be available are asking a valid question: why the early conclusion?