Thread:Ben Stevens2022/@comment-27564979-20160323112910/@comment-27384850-20160323163935

The official translation says "Of course, you can't tame every single monster in the game. Only a few species of small-animal types are eligible." The "small-animal type" is referring to a type of monster, which is a type that Pina fits given its size.

Not sure how that part is phrased in the JP version, though I doubt it's not incredibly similar.