RoyH is correct. ATC is last priority unless it is an ATC related problem.
On the speculation that this aircraft stalled; discounting wind, the 353knots ground speed equates to approx 167KEAS and 172KCAS.
This is not a stall speed for the A/C weight of approx 59 tonnes and roughly equates to where you would expect the airspeed to be in a high alpha situation being managed by the FMGEC.
There was about a 20 knot tailwind at the altitude the aircraft was flying at. Whether this can be factored in depends on whether the aircraft actually entered a CB, as the local wind speeds in the up draught and down draughts would render the calculation moot.
The 353 knot radar groundspeed (if accurate) probably means that the aircraft was very slow, but not stalled.