Spotify currently doesn't have an official companion app for the Apple Watch, but that's about to soon enough. Third-party app developer Andrew Chang had created an unofficial Spotify app called "Spotty" for Apple Watch users that also supported offline playback. After 9to5Mac published a write-up of the app, it exploded in popularity, which brought it to Spotify's attention. Chang was contacted by the music service regarding concerns about the app's name being too similar to "Spotify"; This led Chang to change the name to "Snowy". Shortly after this, Chang was contacted again to be hired...
Source: http://www.gsmarena.com/official_spotify_app_coming_to_apple_watch-news-24506.php