Why do some Gen 2 Pokemon appear in the Gen 1 anime?

Question

Such as Quagsire and Togepi.... I thought they were Gen 1... All cause I watched it
(Until I check the Kanto Pokedex, But I'm still confused)

Answer 1

The Pokémon anime was started after invention and release of the games. I believe by the time togepi hatched in the anime, game freak had already made its design for gen 2 games.
And quagsire was not in the anime of gen 1, it was seen first in gen 2 itself.
Hope I helped!