Shock has paint missing?

[stanmckinney]

I had my tires rotated yesterday. I noticed when the rear wheel came off, the shock on the driver's rear was missing some paint in the middle exterior. It looked as if something had been rubbing against it enough to remove the paint and leave a bare spot.
I have had no problems, no noises, etc.
Can anyone even gues why the paint might have been missing?

 

[orange 07]

parking brake cable rubbing?

 

[LV51FER]

Often just the shock cover itself rubbing against the inner tube. The top shroud is to keep dirt out and it can move and come into contact with the bottom part. Nothing to worry about.