The prefix extra- just means beyond/outside. It lives outside Earth (Terra) so it's extraterrestrial. Though if you said it's not diverged enough to be a separate species that would be a better objection.
> The actual definition of extraterrestrial life is life that did not originate on earth.
While I would not consider something that evolved on a space station around Earth as extraterrestrial, this seems a bit restrictive. This would rule out any life evolving from Earth material on Mars brought by a rover as extraterrestrial even million years later. Also, if we discovered life came from an asteroid, we might have to consider ourselves as extraterrestrial with such a definition.