Question about the Anti Theft alarm

So I’m a pretty new Mini owner. This is my first one, I have a 25’ Cooper S. Yesterday I got an alert on my app that said the anti theft alarm was triggered because it detected movement inside. The taillights started flashing too.
However, nobody is inside and I could see the car from my windows and no one was around either.

Has anyone had this happen? First time for me. I got a bit nervous when I saw that pop up on my app lol 🥲 I guess I’m just curious as to why or how that would’ve happened.