If it happens again then, to help find the ‘culprit’, within 20 minutes of the issue occurring, submit a Sonos diagnostic report from the ‘Settings/Support’ area of the Sonos App. Make a note of the reference generated, and when practicable, contact/chat to Sonos Support Staff about the matter via this LINK and see what device on your network started the playback.
It has been known that pets/small animals can operate a speakers touch controls too, but start with finding the source that caused the speaker to play.
Hope that then leads to the answers you are looking for here.👍