Tailplane stall?
Although we have to wait for the findings of the investigation, it is already pretty clear that is was not a tailplane stall. All indications like stall warning, wing rocketing etc. are typical for wing stall. Further, with the flaps extended only to about 10°, a tailplane stall is very unlikely, apart from the fact that on this airplane tailplane stall very unlikely anyway (except maybe if we suspect total failure of tail de-icing system) . The only thing that hints toward tail stall is that it happened when the flaps were extended. However, that could be coincidence of circumstances. The wing stall could have happened for a very simple reason: low airspeed after level off and gear selection. Gear extension on this aircraft produces considerable drag and airspeed goes down fast in level flight if power is not increased. And the crew may have been distracted by noticing the ice. That of course is speculation at this point.
But, if it was a wing stall for any reason, the crew obviously thought it was a tailplane stall and they did the recovery procedure for that, like retracting flaps and pulling back on the yoke. By that they aggravated the situation until it was not recoverable, due to low altitude.
That may not explain why the got into this situaion in the first place, but it could explain why the recovery did not work.