I'd file it under things that initially sound ridiculous but make sense when you think about it. Which is fine by me, those are always interesting.
It does remind me of shoes on the highway, which is more mundane than a limb but an ocean but turns out to have a variety of mundane to wacky answers.
Also, this line from the subheading is kind of ridiculous:
> How do you lose that in the ocean?
A prosthetic leg is pretty high on the list of things you might easily lose in the ocean. In this case, the owner had been surfing.
Nevertheless, cool article.