Yes, it IS fake. Read the damn Snopes article:
Quote Originally Posted by Snopes
The Bonsai Kitten web site is a joke, not an actual promotion for the making of bonsai kittens. Investigations by law enforcement agencies, including the FBI, have already determined no real cats were harmed in the creation of the pictures used on the Bonsai Kitten web site. Signing a petition to shut down the Bonsai Kitten web site will not prevent any kittens from being harmed, because no kittens were harmed in the first place.
BTW, did you know the word gullible isn't in the dictionary?