Battery test overnight = 13km ran!

So along with my ongoing woes with the battery I did a battery test overnight and before going to sleep I set off a run activity and placed the watch on my bedside table. 6 hours later I woke up and glanced at the watch. I had done ~800 steps and travelled 13km! Eh? The watch has been stationary and not even on my wrist. How on earth can I have done a 13km run while I am asleep and watch not even being worn?