It could be scars, scrapes or injuries. Hard to tell from the pics. Maybe from mouse bites?
Scale rott is normally from bad environmental conditions such as high humidity, dirty/soiled living area and poor air circulation. Basically, breeding grounds for bacteria.
If anyone would like to add on to this or correct me with some facts please do so. I do not know this through experience but only through books. I guess that is a good thing for my captives.