It could still be hypoxia. Have a look at this video of someone trying to solve trivial tasks while oxygen deprived
getting things hilariously wrong while happily being completely unaware of the fact.
(That's why "put on your own mask before helping others" is so important: If you don't,
it is very
likely that you'll be too far gone to help anyone, yourself included.)
The pilot might have tried to unlock the door, might even have been sure he'd done
it multiple times – while repeatedly activating the lookout.
The descent is a bit trickier, but can still be explained by "completely stupid due to
oxygen deprivation": A descent is usually programmed at some time towards the end
of the flight, and he has done so hundreds of times before – so he did it again.
On the other hand, cockpit doors are solid, but not airtight, so the effect should extend to the
rest of the aircraft after some time. That's a point for premeditation.
Man, I so
hope it was hypoxia...