Yeah, Biblo probably can't have a Owl Zoan Fruit, because we already know they have the Nurture Fruit that can magnify the size of things. Unless Biblo is like Blackbeard for some reason, and can handle having more than one Devil Fruit. Like a member of the Davy Clan in hiding or something. But, that's pretty unlikely.
Of course, we never did learn why people aren't supposed to linger on Elbaph. Maybe there's some curse on the island that turns humans into animals? Maybe ALL the Elbaph Animal "gods" are actually humans that got turned into animals? Like the Lion-Cat. That could explain how Louis Arnote or someone else could be Biblo, while also having a different Devil Fruit. The Devil Fruit power and the animal curse could be different things. But...Luffy DID eat the Ear God rabbit. And...I don't think Oda would actually make Luffy a cannibal. So...probably not.
Maybe it could play into "reincarnation"? Maybe Biblo could be someone who died on Elbaph and got reincarnated into this owl? If history really is repeating itself, along with very similar people getting reborn in every cycle, this might be a way for Oda to introduce that concept into this story. Since he really hasn't touched on that too much yet, if it's even a factor here. But, if that was the case, Biblo really shouldn't have any memories of his past life. So, probably not, for a few reasons, really.
BUT...I suppose Biblo COULD be a Mink. Or...the bird-equivalent to a Mink, since all the Mink are exclusively mammals. No reptiles or birds or other types of animals. That would give Biblo the ability to at least speak. And no one ever said Louis Arnote was a human. It's a interesting possibility, at least.
But, the most likely option is still that Biblo is just a "normal" Giant Elbaph Owl that enjoys reading in his free time. I wouldn't be surprised if Biblo was someone's "pet" from the distant past, though. Like how Ragnir hangs out with anyone with the Nidhogg Fruit. Or Zunesha with Joyboy. If I had to guess...I'd say Biblo could be Lili's pet owl from the Void Century. After all, Vivi has Karoo. So, if the royals of Alabasta all have a fondness for birds, Biblo wouldn't be too out of place as Lili's old pet. And he could have developed a fondness for reading from hanging around a royal family.
So, I'm personally leaning towards "Biblo's the pet of someone historically important" like Lili, myself. But, "Mink" is also a interesting possibility. Though, it would be nice if it tied into the whole "don't linger on Elbaph" thing that Oda still hasn't explained, yet.
