Random “Finished your workout?” prompt

The last few days, in the middle of tracking a workout on my Apple Watch, the screen will randomly light up and say “Finished your workout?”

No, I haven’t. There is seemingly no reason for my watch to think I have - my heart rate is still elevated and it doesn‘t happen right when I reach my workout goal (sometimes happens before, sometimes happens well after). Is this just a bug? It started happening this week but I haven‘t done any software updates on my phone or my watch since before Thanksgiving.