PPRuNe should really be renamed "Arm Chair and Flight SIM Wanna Be Airline Pilots" because the vast majority of the so called "experts" on these forums are exactly that and not current professional airline pilots.
Studi,
The aeroplane reverts to Alternate Law whenever a "dual" failure is detected. The failure of the A/P, A/THR and reversion to Alternate 2 Law all occurred simultaneously.
Ironically perhaps but the aeroplane reverts back to being a Cessna 150 whenever the failures are such that the automation feels that it can no longer cope. I say Ironically because it is on these rare occassions when the protections are probably most needed.
In this case the autopilot had at least two or more unreliable airspeed indications and it would be unsafe for the autopilot to continue to fly the aeroplane when it is being fed unreliable information. The protections are also abandoned because they too rely on this information. What's the difference then between the autopilot flying and the pilot flying when both will receive the same limited, reduced and unreliable information? Because the pilot is human and hopefully has the ability to recognise and reason out the solution based on the evidence available. First and foremost he must take control and fly the aeroplane.
If you bother to read the other interim reports produced by the BEA then you will know that the very many previous occurrences of this issue have resulted in the same symptoms and an almost immediate stall warning occurring. Partly due to the abrupt change in measurements (pressure) and also due to the turbulence that was encountered.
The margins that an airliner flies within at 35000' are pretty small and a pitch attitude of 10 degrees nose up would never be seen in normal everyday operations at this altitude.