Okay, so I emailed the creator of Wilber, Tuomas Kuosmanen, about what Wilber really is. My email to him is as follows, copied and pasted:
Tuomas,
Are you the same person that designed Wilber the GIMP? If so, I have a question. Is Wilber supposed to be a known animal, or is he a GIMP, as Gimp.org says? Some say he's a coyote, but I tend to believe what GIMP.org says. Could you please clear this up for us. GIMPWIKI says he's a coyote as well, so some believe that. Also, did Wilber ever have a body, or just a head, as it's known now? Please clear this up for me. Would be great to hear it coming right from the person's mouth that created him. Thanks!
Jim
His response, also copy and pasted:
Hey, yes I am. :-)
You are correct: Wilber is an animal of its own species: a "gimp".
What a GIMP is, is sort of a joke, because people kept asking it so
much: it would be so boring to say it's a dog or a fox or whatever.
And when I designed the character, I did not really have any
particular animal in mind. - so it's sort of a mystery without any
explanation.
It also does not have a body. I think I have seen an image years ago
when someone did a body for it, but not in general.
Have a good day! :-)
//Tuomas
So, GIMP.org is correct.