I don't know what happened really, but normally to get financial partners and raise the large amount of money needed for doing an animated movie you prepare a k

I don't know what happened really, but normally to get financial partners and raise the large amount of money needed for doing an animated movie you prepare a kind of trailer or short clips to show and convince them, usually way before the script is finished, and probably not for the general public. I guess that in this case that "trailer" was good enough for showing as a first public teaser trailer, even if it was not entirely faithful to the final script.