well, at least that explains why he's hiding... Tetraodon cochinchinensis is sedentary, territorial and antisocial, but stays relatively small (~7 cm). Aren't you lucky they just got you the one?
it depends on what you want to do. when you were ordering your puffer, did you purchase a "red-eye" or a "carinotetraodon lorteti"? unless you used the scientific name, its a buyer-beware situation. however, there can be no confusion whatsoever between the two species.
i don't see you being able to get the kind of puffer you want without having to give back the puffer you've got.