A/P drops out at 1 degree above Alpha Prot in normal law, you can still get back to Alpha Max with full back stick and the A/T out (Alpha Floor) which is still short of Alpha Stall albeit not by much. In alt law Vsw or the Alpha that it triggers at is higher than Alpha Prot so although the warning is there you still have a little way to go to the actual stall. In severe turbulence close to max alt you will get transitory spikes in AoA (which is why you disconnect things if its bad enough and hold the attitude) so in Alt law at turb mach with an aft CoG you could well get a couple of transitory warnings as the AoA threshold is temporarily exceeded and not be particularly close to the stall. Certainly with TOGA and full aft stick given the lack of damping you could get a pretty decent rate of climb for a short while at least.
So I figure they were in Alt Law from the point the A/P and the A/T kicked out and it was the PF's roll and nose up demand that triggered the initial 2 blips of the stall warning which would have triggered at a lower AoA than in Normal Law.