For Chespin, just because it used a move that appeared similar to a dark type attack does not mean it will be grass/dark. Many Pokémon can learn moves that are of the dark type, such as Scizor with Night Slash, but the Pokémon itself is not a dark type.
Finally for Froakie. In the trailer Froakie appears to be using a move that hits several times. I believe this move to be fury swipes and not a flying or fighting type move.