In my opinion, and it is just an opinion and not based on fact, either VS or FLC could have yielded this event and along with the AOA indicator were red herrings. This plane was clearly flying too high and too slow for the given conditions and the pilot took his/her eye off the ball.
Each aircraft has a climb schedule speeds and above specific FL the climb should be on a specific Mach number.
If the pilot was maintaining the required Mach then the aircraft wouldn't have stalled...
Once he passed a specific AOA (which he wasn't aware of) due to the fact he was climbing at 1000ft/m at FL410!! and assuming he was leveling at that altitude it would have taken him quite some time to recover the speed but he was continuing with his climb and that led to the stall.
If he was keeping FLC .something that was giving him the protection...