I don't cheat but I've had two days now since buying my first watch in April where I was credited for things I did not do in the activity app.
I have three watches and I frequently will take one off in the middle of the day and wear another. On Mothers day, I did this and immediately upon putting my ceramic watch on, I was credited with the Mothers day award and I had not gone out walking yet and I didn't even have any minutes in to qualify but I got the award.
Monday was my second day off as I have Sundays off too. I was lazy and didn't expect to fill any of the rings except for the stand ring. I had one of my watches still paired to my 6S so I unpaired it to use with my 6S+ that I normally use for exercise. As soon as it was paired and setup, I was credited for all three rings and I should have only gotten the stand one filled. Check out my screen cap from the activity app for this day. Notice there is no exercise in the graph but the ring is still filled. I also only had about 300 calories in but it gave me 417. Not sure where it got the stats from for the rings.