Autotrim
It would seem logical to have a slight time delay in activating autotrim.
When you make a demand on the elevator, that needs to be in the context of the aircraft's current trim.
If the aircraft were to quickly trim while you were making a pitch input, the aircraft wouldn't be in the same trim when you relaxed the input.
The idea must be, lets wait and see how serious the pilot is about this control demand. If he keeps it up for say 5 seconds, he must be serious, so we can trim some of the back stick out.
But in the case when the nose down control input returned airspeeds to functional in the deep stall. The stall warning return probably discouraged the nose down input inside of the delay time. Therefore the THS did not move toward nose down.
The actual aircraft control logic is no doubt proprietary to Airbus. We will only get applicable snippets of it in the control analysis when BEA finally publishes. There are probably clues in other AB accident reports how the thing works.