I don't know much about the details regarding these creatures yet, but I know that they were originally belonged to another world.

And from what I can tell by those Poke Balls on the floor, I can say that proves that they are not Pokemon.

[Of course, if Guzma refuse to believe on his words, then he has no choice to but to prepare for the worst. Of course, he does have a secret weapon (or ability) in case he will keep using the Poke Balls against the poor Chocobo.]