In the question Has an anime ever come out before the manga was published? it became quite obvious that there are indeed several animes that air before their manga has been made.
But this also made me wonder about the following:
Does this imply that all anime that air before a manga of it exist should be considered fillers?
Fillers are non-canonical material, which usually implies it did not happen in the manga. Or as Urban Dictionary stated it
A segment of anime, whether it be an entire episode or part of one, which does not appear in the manga of the title. Fillers, as the name implies, "fills" an episode with non-canonical material which has been written usually by the same company which animates it.