@ Arve: yes, that does help, thank you! I can now assume that it's probably supposed to be this way.
Nonetheless it seems a rather peculiar game design, to make the item that teaches you a pet Rare, while the pet itself is Uncommon. That would only make sense if there are other sources to learn that pet, which I doubt there are,
(BTW I would have bought them anyway;; I consider the rarity of non-wild pets just an additional stat, not a do or don't. I do have to differentiate concerning wild pets though,, because my PJ is full. I even had to release a Poor pet, to make place for the Jade Owl