This usually happens when I turn off my Bluetooth but whatever music I'm listening to will change to something that I have never selected. Not only that but it will keep trying to play that unwanted music on other devices that aren't mine. I'm not sure how to fix this.
We understand your concern about seeing someone else’s device in the connect picker. Don't worry, our Accounts team can take a closer look at this to help you out. You can get in touch with them from any of our social media help sites: @SpotifyCares on Twitter and Spotify Cares on Facebook. Just send them a private message with your account's email address and username.