Demonic cleaner or falsely accused ??

I was visiting my brother in law who has a rectangular IG, vinyl liner.

I noticed he had perhaps a hundred or more little round liner patches in the corners where the walls and bottom of the pool meet. Liner is only 2 years old.

Company who installed the liner claims the Robotic cleaner had done the damage. Cleaner appears to be same design as an Aquabot, same rotating scrubbing roller in front and back.

So he sent cleaner in for service and was sent a replacement, but never heard if it was in fact, defective.

Has anyone ever heard of any cleaners doing this kind of damage?

Any thoughts on other causes or contributing factors?

Thanks