"Ease-hike-trim" is like the standard response to a gust when you are sailing upwind.
Easing reduces the heeling moment a bit, but also, when a gust hits, the apparent wind shifts aft a bit.
(Red/pink is the condition before the gust)
Therefore, letting out the main also improves the trim and the gust can be translated into more speed.
As the boat accelerates, the apparent wind shifts forward again and the main can be trimmed in.
This assumes that the gust only brings a change in wind speed. Often the gust will also create a change in direction as gusts are in many cases faster winds from above that come to the waters surface as part of turbulent motion in the air mass. (At other times, gusts can be vertical, falling wind that spreads out when it its the waters surface).
Winds that are not at the level of the water can be blowing in a different direction (wind shear) and that brings a change in wind direction during the gust; that direction is independent of the shift of apparent wind and can go in either direction.