You can do all sorts of things in Apple HomeKit that would affect the Sonos.
In the Sonos software, there can also be alarms set that would start a specified station at a specified time.
If your family ever had a person over that used Spotify Connect while on your network, that would stay ‘connected’ to your system until such time as it was broken by playing any non-Spotify stream (such as Apple) on your speakers.
If, within 10 minutes of this music stream beginning to play, a diagnostic was submitted, you could call Sonos Support directly to discuss it, and they would be likely to be able to tell you what submitted the ‘play’ command.
Have you ever authorized a 3rd party app to control your Sonos system? If so, there's no easy way to deauthorize and you'll need to talk to Sonos support.
Something like that just happened. My Arc is wired to my TV. TV was off but suddenly music started coming out of the soundbar. When I turned on the TV, the Arc worked normally.
Do you have a cable box connected to that TV? Both cable boxes and TVs have been known to “come on” without intervention when they’re updating their firmware/software.