Yes and no.
It is a great prerequisite for getting used to allowing the board to ride more independently underneath of you but I really did not get into unweighting with this person yet as it is a little ways past their current progression.
To answer your question more specifically, the unweighting is something a rider does deliberately to release their edge so they can then switch onto their new edge to initiate the next turn.
What I am having this rider do with the flexion and extension here is actually just getting them used to the timing of doing it. In reality for using a true down unweight, the rider hold off on that last final little bit of flexion and then does it abruptly at the exact moment they make the edge change.
The opposite of this and one most people very instinctively do is an up unweight where they will actually pop up and release their edge almost like a leaper turn. This works well on mellow terrain but is not something a rider wants to do on really steep pitches. The down unweight allows the rider to release their edge without popping themselves up and away from the mountain side and then trying desperately to get their new edge engaged again. The down unweight is a mush softer approach, like you would use if walking on glass.
I have a new video coming out that goes into this in depth. I just need to edit and post it