No its never been directly stated how or when kakashi awakened his msmy theory is that you have to experience a ms level jutsu with at least a 3 formidable sharingan. And then you have to train yourself on the rest. The reason for this thought is because both kakashi and sauske, possibly Itachi were all exposed to such conditions. With the correct sharingan. And then had ms level techs soon after. But kakashi jot being a uchiha he had to work harder and train more to achieve the end result of kamui.