Pilots who have flown A330, and who have posted on these forums, have pointed out that at high altitude, the aircraft requires a light touch to hand fly.
Pilots who, actually, flew "ALT law" at high altitude, reported difficult control of the a/c.
From what we see, bank angle control required
VERY large ss inputs.
In this situation, it seems difficult to criticize large ss NU inputs by PF.
That can explain the initial nose up, if the aircraft was not Straight and Level at the point of "you have it, robot taking a timeout, old chap."
Imho, the initial nose up is a reaction to the loss of 360' (35,024'-34,664') in just 4 seconds (02:10:05 / 02:10:09) that is "
only" a 5400 ft/minute rate.
Any pilot flying an RVSM route will react very quickly to this kind of altitude variation.
It does not explain subsequent nose up inputs that lack successful counter-corrections toward a more level attitude.
I am afraid we will never have the answer to that question.