This isn't due to the Puppy Cave being special per se; it just has a bit to do with how drops work. Puppy Cave has two high monster intensity levels, 5 and 6, on which the PC will get many more kills than average. In addition, lesser vaults like PC:6 have atypical item drop rates. On average, completing the PC will give a fair number of items simply because you have to kill a lot of monsters to get through. Particular items (eg. spellbooks) are no more common in one dungeon than in any other, however.
I always like checking the Puppy Cave as a caster because I've always had very good luck finding shops there. I might speculate on reasons why there could actually be more shops there, but it's probably just positive bias on my part.
Any time a player finds Executor and fails to use it, the RNG kills a cute dog.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Monk, and ULE Priest down.