Look at the teeth. They have a max penetration of a 1/4" (7mm). It scraped the skin off and maybe the top bit of muscle. Their suck is more devastating than their teeth. They're just big fairly dorky catfish. Look at this doofus:
Interesting that Frazier Nivens is the photographer on that nurse shark feeding dive. We did 2 or 3 dive vacations with Frazier in the Bahamas back when he was proprietor of the now gone Nassau Scuba Centre. They were great trips and I have a lot of respect for Frazier and many good memories of those trips.
We were not at all interested in doing the shark feeding dive with Gray Reef Sharks that was offered by NSC but we strongly urged to try it out by the divemasters, so we finally decided to sign up. We may have been mistaken but at the time we felt the divers that took part in the shark dive were treated as "elite club" and were more likely to be taken to the better dive sites.
It was an interesting experience, we were over-weighted and we sat in a circle watching the shark feeding. We were instructed to keep our appendages tucked in and not to touch the sharks. The divemaster was wearing chain mail while Fraizier took the video. The divemaster used a pointy stick to feed the Reef Sharks out of a bucket, but a Nurse Shark kept coming in close and he would feed it by (mail-gloved) hand.
Things started out slow and tentative and then the sharks went crazy! They grabbed the bucket of food and fought for access. A Grouper hovered next to me to watch and waited patiently for the frenzy to end so it could move in to grab the scraps. I liked that Grouper best of all.
It was a memorable dive but I still think that it is a mistake to teach predators to associate food with people. Consider all those stories about idiots that leave food around when there are bears in the area., or even try to feed the bears!
I know that when lionfish first started invading the Caymans there was an early attempt to teach predators to eat lionfish to try and control the population, but I think that most folks have now figured out that isn't such a good idea. It just taught them to look to humans for a meal.