The story says he had the leash around his ankle, white water leashes attach around your waist like a PFD rescue vest line with a buckle and string with a ball on it to release. I've used mine and had to release it once in a playpark when my board was running rapids without me. It was intense but that guy didn't have the right gear, he paid dearly for it
I leash my board on white water, I could see not using a leash if I was running class IV or something on it but it's pretty easy to reach my cord on my waist when I need to let go of my leash/board.
I even have a convertible leash that can go around my ankle or waist.