This is exactly what can happen when scope rings are not lapped properly - what you are seeing is what happens when the contact points are not uniform between the rings and the scope. From the little that I can see from these photos, here's what I can offer:
- Indentations on scope tubes can and do occur when you have proper torque, when those pressures are put on a much smaller surface area than the rings are designed for, which is exactly what happens when rings are not lapped. The sides are just not perfectly parallel with the tube, and more pressure is applied to a smaller area. The effect is similar to how much more damage will be done to your foot if a woman steps on it in high heels vs flats.
- The rough surfaces of most scopes reduce overall surface contact, as there's just less of the scope tube in contact with the rings than if those tubes were smooth. Microscopically, it looks like a mountain range. It may feel like it has more 'friction' being rough, but those metal asperities (the peaks and valleys of the metal surface) are what have broken off in the photo. The peaks have literally been removed where the bare aluminum appears. This is minimized by maximum surface contact with the scope rings. But if rings are out of alignment it can enhance this wear through a type of friction wear called fretting (think vibratory rubbing and the wear it produces).
- The strange coloring that looks like adhesive is likely, at least partially, the result of rub-wear/fretting and the oxidized aluminum dust that wear produces.
- Look closely and you can also see pinpoint spots of greater wear, a couple of which almost look like pitting. That can be fretting on a high spot, but it can also be the result, possibly, of some of that oxidized aluminum being aluminum oxide, which is much harder than the aluminum substrate. When you scratch bare aluminum it oxidizes pretty quickly, but that aluminum oxide is very hard. With fretting, once it starts it can start accumulating and, essentially it turns into an abrasive. A couple of pieces of that grit in a fretting/vibrating situation can cause pitting.
- The strange wave-like patterns may also be an indicator of fretting, with the vibratory oscillations causing that wear pattern.
