So lemme get this straight....if the ocean just all of a sudden just began to recede and the beach shore was sucked dry....you arent going to get the idea to...oh I dunno.......run?
I would, if I happened to be on the beach at the time the water started leaving at a high rate of speed... However, the tsunami came in at a little before 0800 local; most people weren't awake to see the water recede.
So, you wake up in a hotel room at 0745, see the nice HUGE beach that you've never seen before in your life, and decide to go for a swim before breakfast. How, exactly, is a tourist supposed to know what a beach is supposed to look like when they've never been there before?