Found this link the other day. It better explains how the snowboarder got separated from his crew (different lines through tight trees & the others got below & couldn't find him). You can see the skier's buddy at the beginning of the video.
Some folks on this thread mention him skiing over the snowboard - I don't see that. Think he just saw the bottom of the snowboard sticking up.
A Washington state snowboarder is recounting the moment he was rescued by a skier after he fell into a tree well while snowboarding near Mt. Baker
komonews.com