Quoted By:
They probably just wanted to show something they were gonna introduce later, like Ho-oh
but then decided not to
Or maybe it's a reference to something, as a dumb joke
maybe the franchise started with them wanting pokemon species to not be limited to those included in the pokedex
or they just wanted to fuck with the readers and make them ask "what the fuck is this thing?" forever and ever
So many possibilities, most likely we'll never know for sure
