If I am misreading some recent posts, I apologize, but there seems to be some confusion about stall warning and airspeed. The sudden drop in indicated airspeed was due to ice particles blocking the pitots, not due to a real speed reduction. Stall warning begins when the AoA exceeds approx. 4 degrees, and that threshold was exceeded at several times. AoA reached 16 degrees at 38000 ft, indicating that the airplane was definitely stalled at that point.
Stall warning, followed a few seconds later by uncommanded left/right rolling motions probably accompanied by heavy buffet is usually accepted as an indication of "you are now stalled".