Could it be to spring load the sail to get a cleaner and faster rotation? First he goes a little downwind to get max speed, then he turns a little upwind as he comes over the board to spring load the sail before he releases it into the rotation.

Many people going from vulcans to spocks have to learn to sheet in the sail before poping. In a vulcan you can get away with a sheeted out sail, it can even help you not rotation more than you want, but for a spock you need to pop from a sheeted in sail to help the rotation.