There is a bit of a "new science" of unsteady aerodynamics which indicates that high pitch rates can cause flow to remain attached until rather higher AoA values than would normally be indicated by theory or conventional test techniques. I don't honestly think it's a player here, since any warning triggering at the normally determined stall AoA (plus whatever is considered the sensible safety margin) will be safe.
I spent a while last year testing a new artificial stall warner for an aircraft which had a particular stalling problem (60° wing drop, undemanded incipient spin, the usual suspects). The device (which worked well) was a spring-loaded vane parallel to the leading edge which operated when flow started to detach, releasing spring pressure. We actually looked quite deeply at deceleration / pitch rate and interestingly once it was in a setting we were happy with it was giving a more or less constant 3 seconds stall warning at any deceleration rate from 1 kn/s (i.e. about 3kn) to 5 kn/s (i.e. about 15 kn). To what extent that was unsteady aerodynamics, and to what extent it was other factors, I'm not all that sure.
I'd prefer for the usual reasons not to identify the aircraft, but the stall warner is at
http://homepages.which.net/~aci.stw/ and an interesting piece of simple and effective design.
G