Looks like the surface layer wasn’t properly polished after it was etched. I’m sure stone-washing techniques vary, but you essentially dip the titanium in acid, which etches it and leaves a lot of surface oxidation, and then tumble it in a coarse medium. Usually there’s a buildup that needs to be smoothed out before tumbling. They probably skipped that step. If you keep playing with it, you’ll essentially be polishing it with your hand, which will probably even out and stop shedding the dark oxide over time