No Weaknesses When on the Bench

Not really sure if this is a bug, but decided to post anyways…

I have an electric deck with Zebstrika, who has an attack that can hit any Pokémon, even on the bench, for 30HP. When I attack the active Pokémon, if it's a water type, it'll lose 50HP, because of it's weakness to lightning which makes it +20HP of damage from lightning attacks. However, if this same Pokémon were to be benched and I attacked it with Zebstrika, it would only take 30HP. I don't know if this is a bug or a rule in the regular Pokémon TCG, as the release of Pokémon TCG Pocket it the first time I've really interacted with the TCG in a while.