(As far as I know the stall warning is inhibited because the AoA vanes do not work below 60 kts. You cannot sound a stall warning when you have no working sensor to detect a stall.)
You obviously haven't been following these threads.
According to many prior posts here, the Stall Warning shuts off below 60 kt IAS. Why they have IAS input to SW is beyond me. The DC-10, for example, uses only AOA for SW.
Regardless of IAS, the plane was moving through the air fast enough to keep the AOA vane aligned with the relative wind, even as they were falling like a brick.