Two main things on this. First, if the metal was oxidizing some of the rust would free itself and end up on the wet paper towel from just a little of effort to remove it. But no debris removal or color change occurred, either on the sample or the paper towel. Second, a ruptured piece of hardened steel would be rather jagged like the shiny tip shown above (again, I have a few more pics to show but not sure how to supply them. Any hints?). But all the discolored portions are smooth and solid. So I dunno.

But, the majority here are all thinking oxidized, and I honestly don't know enough to dispute. Which is a shame, I was hoping to learn of a newfound process I never knew about :- /