In certain example embodiments, a coated article includes respective layers including diamond-like carbon (DLC) and zirconium nitride before heat treatment (HT). During HT, the hydrogenated DLC acts as a fuel which upon combustion with oxygen produces carbon dioxide and/or water. The high temperature developed during this combustion heats the zirconium nitride to a temperature(s) well above the heat treating temperature, thereby causing the zirconium nitride to be transformed into a new post-HT layer including zirconium oxide that is scratch resistant and durable.