I apologize for sounding opinionated but I don't believe for one moment this crew with 6000 or so hours between them simply forgot to add power and stalled the airplane.
I listened to the NTSB statement again. It sure sounds like the "upset" occurred while flaps were in transition -somewhere between 5 and 10-. This sounds an awful lot like "result" was not such a poor choice of words after all.
I also listened to the ATC conversation (you can find the recording online). They were at 2300' for a while. If they did not power up when they leveled, seems to me they would have got stall warning long before -and, from what I understand of the DHC8-400 ice protection integration into stall awareness -which they selected- , the shaker was triggered 20 knots early. Could it be that their low airspeed was due to rapid ice buildup?
For the most part, it sounds like the crew did everything right. They were aware enough to switch on deicing equipment. They reported significant ice buildup to ATC. Do you really think the both of them forgot about the power levers during this time?