Maybe a naughty neighbor walked up to your door and yelled at HomePod to play something? After all Siri on the HomePod does not have voice recognition..
No cat lol.
On the flip-side, i left mine playing music yesterday evening and it is still playing when i got home this evening about 24hr later.
Why wouldn't it be though? If you never stop it, why should it stop?
Is it possible to start the HomePod playing remotely by tapping on its icon in the Home app?
I have no idea why. I’m sure the neighbors love me lol.