I am also curious... but I did notice drag marks in the direct center of the tire indentations.. Looks like it might have been engine failure and the drag marks were probably the propeller stopped.... notice how it is every few feet... I think the pilot was doing the best he could (flaps) in keeping the plane upright against the drag from the sand.... AND, he and the passenger are both still alive :D
As they say, any landing you can walk away from is is a good landing. In this case if it was engine failure, something to think about is getting the prop to a position, using the starter, and if the engined will rotate, where it will not strike the earth tip down, if you tip up. That action does require time, and a really clear head in an emergency. It isn't something people in single engine airplanes practice much.
Speculation is NEVER advisable, .....
....... so here's what I think happened.
Shoals Pt. is 10 miles west of Sitka airport. The 185 is registered to a Sitka resident (looked up N3332S). Probably a training event...(the skip marks between the main tracks is the tailwheel) ....takeoff run and notice how the beach is dark and disturbed ('rototilled') under the prop and it looks like he encountered a soft patch of sand just before it got light on the gear. The tailwheel would have been leaving a much more continuous track and braking would have left different (darker in the wet sand) tracks if it was landing.
Looking at the marine charts (free viewer and chart downloads at maptech.com) the beach at Shoals Point is open to the North Pacific, and I imagine calm days and low tide don't always occur when you've got time to practice off-airport landings and T.O.s.
There .....I've speculated, and NOW I'm going to the FAA Preliminary Reports to get more info.
Honest.