Are anime that air before a manga adaptation considered filler anime?
I feel there's a bit of misconception here.


Fillers == Not canon
Canon == Original material from the original author.


There are episodes in Naruto for example, (like Naruto episode 101) which are canon but were not in the manga.

So the question of whether content being filler or not has nothing to do with it being in one medium or another (although there's usually a correlation). It's about who made it.