I think the problem in the video is that the crew lost control of the spinsheet while getting got by a wave.
Getting your back foot out of the strap will be impossible if your front foot loses contact with the hull, no matter how tight or loose the straps are.
Just bad luck really.

Some kitesurfboards use so called "skyhooks", it's like a hook where you can put your toes under to lift the board out of the water, could work on cats as well.