Interestingly, he (This guy) makes the movement both times he loses the edge and becomes unbalanced. When looking at arm movements, I always consider two things, the momentum of the moving arm and the equal and opposite reaction (on the body's mass). I think he is swinging his rear arm backward to help move the torso forward (in relation to the lower body) to become more angulated to recover balance.
In the original video, the rider makes the arm movement as he begins to angulate for heel side turns. At 1.07 The arm movement is exaggerated to recover as he almost loses the edge. and at 1.23 he mistimes or overcooks the arm movement causing the board to auger in. Generally though for same reason as above, to help move the torso forward (in relation to the lower body) to become more angulated.
As Jack says, the counter rotation on the toe sides may be a factor, perhaps causing the late angulation on the heel sides.
In case anyone doesn't know the keyboard short cuts for Youtube.
j - 10 secs back
l - 10 secs forward
Arrow left = 5 secs back
Arrow right - 5 secs forward