Sigh... I think one of the lessons that most reefers will tell you is that to take all advice from LFS with a bucket of salt. Its best for the hobbyist to research from updated marine books or the internet.
Puffers are carnivorous. They eat corals, sponges, small fishes, sea urchins and other echinoderms like starfish, sea cukes as well as other small crustaceans like crabs, shrimps and snails.