I think if you landed anything on a soft sand beach without tundra tires it'd flip. I guess he was just unlucky to not have had the problem on an outgoing tide where he could have had some hard packed sand to land on - then again it may have ended up the same way anyways...
 
I'm amazed he put the gear down. The chances of flipping would have been greatly reduced.

Tom
Down and welded RV-4