Yeah, I see that in the video as well. To me, it looks like they are in fact using an up unweight at edge change as well. CASI and AASI have some very different approaches and this may be one of them. Up unweighting is not "wrong". it is just another way to get the job done. AASI`s position is that on steeper terrain, an up unweight tends to pop you too hard off of the side of the slop in a fully extended position while a down unweight releases the edge but allows you to move closer to the surface while doing it.
A down unweight is just a brisk dropping of the upper body down toward the board. This is usually done from a mid flexed position not full flex so in reality, it is a subtle movement. The idea here is in a cross under turn, your legs reach maximum extension as the board travels through the apex of the turn and is at its farthest point from you. In order to maintain a quiet upper body, you have to retract the legs as the board now travels back toward you.
As the board passes just under you, a brisk drop or sucking up of the legs, momentarily will release the edge hold by making the board nearly weightless for an instant. At this moment, the rider instantly tilts the board onto its opposite edge, and then extends through the next turn.
Sometimes this movement creates a slight drop then a noticeable rise of the upper body that looks just like an up unweight. What people generally are seeing is the noticeable upward pop as the rider resets the edge.
I am going to video some extreme examples of this down unweight move and an up unweight in the very near future....