Any chance this was a hotel with an app that uses location services, thus using your own device to query your physical location? I wouldn't like that to be the answer, but the technology exists and legal protections are few. (Personally, I only switch on location services when I'm actively using Maps or similar; it's on for maybe a few hours per month on my phone.)

I hate the idea of being auto-checked out, especially since I like to load my luggage in the car as soon as I'm dressed and ready, then return for any free hotel breakfast I've already paid for it. I'm more relaxed if my gear is stowed away. On the other hand, I'm enough of a coffee snob to go pay for a proper espresso if there is a specialty shop nearby; I could easily imagine being gone for an hour that early for coffee without having intended to check out for the day.