Salmo,
According to the guy who filmed it, the shark snapped it off. He didn't mention if it head butted it while it was buried in the sand or broke it off on the boat chine.
It always gets interesting when a big shark shows up while you're wading the flats. I had a extra large mofo swimming around me a few years ago in the Turks & Caicos.
Good luck on your trip.
SF