Spot on the money Kiwiconehead, as always
Blackhand, when you wrote "retarded to beta gate" - did you mean the flight idle stops? If so, it's quite normal to be at, or very near the flight idle stops on a 2:1 descent when at, or near Vmo. At other times, of course flight idle may be necessary for quick speed reduction (though normally in conjunction with Condition Levers MAX).
I can't quote on this particular instance, but in 13 years of flying the Dash, I have never head of a failure of a power lever trigger, nor of any inadvertent activation of same in flight.