I can only guess that the "surge" of power was as the aircraft leveled off, especially if still in a clean flap configuration (i.e. the power adjustment would be much more noticeable).
I would add that a descent conducted at idle plus the above quote would make for a very noticeable "surge." If the aircraft was very light too (low passenger numbers, at the end of a flight) that'll play into it compared to the same aircraft but heavier.