As we already see many Pokemon using it at distance in the anime, we see that can be trowed like a "radouken" in format of a moutch, like the heart shape of the atract. And most moves who are used from distance are special, of course there are physical moves who can be used at distance too, but they are more based into solid things like rocks, not energy, flame, water, etc. That move have all the traits for being both special or physical, just like water shuriken, is a shuriken made of compresed water and is hard as steel, so it could be both. But a move can only be of one type, special, physical or status, so even if the move can fit in more than one style of move type, they have to choose wich one. I believe the choice is special because most fairy types have higher special stat than physical, so it would benefit most Pokemons. Just like water shuriken were physical and become special, since it has traces to be both, putting it as special would benefit better from greninja higher special stat. But if the move have only traces of the physical stat, like wing attack for example, then they wouldn't put it on special class even if would benefit a particular thing.