I was listening to music that I had saved to my queue.
When the last song was finished I started hearing music I wasn't familiar with, yet it was a style I enjoyed. When I switched back to Spotify a notification banner informed me
"When your music ends, we continue playing similar songs for you. You can turn this off in Settings."This is a fantastic message for 2 reasons. It explained behavior from the system that I didn't request, and it explained how I might modify the system if I did not want it.
Spotify