They're likely referring to the sound effect. The damage sound effect changes depending on whether a move is super-effective, neutral, or not very effective.
That said, it doesn't matter in the case of Nature's Madness, because it deals fixed damage, and fixed damage moves always use the neutral damage sound effect (since they cant score super-effective or resisted damage).
Oh yeah, I totally forgot it cuts the opponents HP in half. Thank You!
Well if that is the case then it most likely is a Fairy-type move based on Tapu Koko's typing. I doubt it is Electric. Most of all I hope it's not signature. They didn't really make that clear. They just said "A New Move... Natures Madness!" I think there is 50-50 chance it isn't signature. If not then there are so many pokemon that can use this, like Popplio3!