I spray painted my 690 last year. Definitely not stolen. The thing that makes me agree with the OP in this case is the overspray onto the license plate. I did a half (1/4, maybe) ass job of painting my bike, but I still removed the plastics from the bike to spray them. Sure, it might not be stolen, but it doesn't hurt to check. :dunno
The instruments were sprayed over on this bike , also the front headlight was sprayed. I guess you could have a friend playing a prank on you and spraying your bike.