Like many home/IoT services, Spotify uses mDNS to enumerate and announce its peers when they are L3 local but they are also controllable remotely by dialing-home to their API albeit with a slightly longer delay. Spotify is hilarious when playing from the Everywhere group (all devices) where desktops, tablets, phones, the thermostat, stereo receiver, and Amazon Echo devices all insist on playing out of time like a crowd of teenagers singing a song.
