Kinda like the suspension on a car. Probably adds a bit of dynamic stability.

In the first half of the vid, the board was further down on the starboard tack - I presume more of a pointing mode.

Later, on the port tack, the board is further up with quite a bit more spray off the side. Looks like they're going a good bit faster as well. Perhaps reaching.

Impossible (at least for my amateur eyes) to judge true wind direction from the vid. Video mentions 12-14 TWS, but the water/waves don't look like it.