Ugh...that was a graphic picture to sip my morning coffee to.
Human teeth are designed for an omnivorous diet; Blunt, chisel-like teeth in front for nipping vegetation, sharp canines for tearing meat, and flat molars for grinding. I suspect this fish is much the same, and the "human-like" teeth are just for scraping algae as food, or nipping off sea plants.
See the teeth on this puffer fish?

They're not teeth in the traditional sense since they're joined together; They're sort of like plates. If you could see from the side, you'd see that the front teeth slope down, just like the "human teeth" fish. The pufferfish uses these unique teeth to pull algae off of rocks. I think it's safe to say that that's what this fish does as well.