It's a pity they got it wrong. When in confused state, one would try everything to save the situation. They must have thought stick aft at full thrust was working since the stall warning actually stopped blaring. The thing they couldn't resolve was why were they still descending at a rapid rate? That's when one of them pushed the stick forward, which unfortunately re-trigger the stall warning. So they pulled the stick back to silence the horn, and the action did silence it. And all the while, they didn't have a valid 'speedometer'...
It's not clear that the stall warning stopped as they descended. All the report says is that it started up again as the speed increased, not that it later shut off. We will have to see the final report to see for sure.
The ASI only were out for a matter of 60 seconds, according to the report, so they had valid indications for the last 2 1/2 minutes of flight, though they may not have recognized it or trusted it.