According to a source from one of the brands of android wear watches, Google did/do not allow the implementation of Spotify offline mode. The only standalone solution permitted is GPM. Why can not Spotify be straightforward and lay out the truth?
According to Deezers blog their Android Wear App supports to store songs offline. this means you can use an Android Wear watch with Deezer as standalone. So I don't believe that Spotify is not allowed to do the same.