It is possible that whatever coating was used was done to replicate the coating on the authentic .. I mean Zen uses different special finishes etc on all of his devices, and whatever that original finish consisted of, aesthetically it does match the tone and texture of the authentic Zen, just google pics of it.
I still need to ask Robbot, but in hindsight this now makes more to sense to me in that Robbot sent me a picture of a 18650 prototype that they were working on, and one of the things that I noticed was that the tone and texture of the raw prototype was obviously different than my finished Robbot ZNA ... this is what the 18650 prototype looked like unfinished ..
which does not at all like the final finish of a completed unit