Its unfortunate most don't take care of things (car) as you would. Can only guess a mechanic most likely had dirt or something on there gloves when taking the wheels off. Or reached in with tools through the rim trying to save time of taking the wheel off. I have learned now before sending my car in for specific things i take dated pictures of that area. If there is any issues i take the photo's to the manager to show them. It a cut a dry issue then. Sad it comes to this but makes life less stressful when arguing who caused the problem/scratch.
One other possibility - did you have your dealer wash the car? I always ask not to have them wash it. Had to buff out scratches they put in the paint once and last time.
