Based on this photo and what was cool when the watch was released, my hypothesis is that this was a ti case with a relatively thick ceramic coating. A thin DLC/PVD coating would allow the underlying metal treatment to show through (brushing, polishing, etc.) but this looks more like a thicker spray on / bake on coating like a Cerakote which completely covers the base metal finishing. No idea what the formulation is but usually these spray on finishes wear over time but can be stripped and reapplied. I think of them as good rust prevention (which ti doesn't really need) and a sacrificial aesthetic layer so instead of polishing the case would be stripped and re-coated if it started looking rough.