Apple Watch Series 10 suddenly displays “Done” in orange

Was watching TV last night when my Series 10 watch suddenly buzzed, and displayed the word “Done” in large letters on an orange screen. I didn’t ask it to do anything. It had a couple of icons (a tick and an x, I think) at the bottom, which I pushed and it came back with a watch face, but a completely different one to the one I’d set. Had to reset that, and it’s been ok since.

Any idea what’s going on here!