"Works for" and "ex-employee" don't sound military. He may not be an officer at all. Perhaps he's a civilian scientist who does work for Starfleet (see: Carol Marcus, Wrath of Khan version), hence him not having a coloured smock over the generic black shirt.
Or maybe he removed the coloured smock as a symbol of his independence from Starfleet, like Kirk in the Mirror Universe sotryline in IDW's comics. As for the terms used in the article, sloppy writing.