He obviously didn't copy it nor is it possible to do so.
Kakashi has seen both Amaterasu and Tsukuyomi, He also saw Ms sasuke's susanoo and even enton, also You do not require Uchiha Dna/chakra nor body to unlock and use MS techs, kakashi using kamui is proof of this. So if it applies to Kamui why would it not apply to others such as Amaterasu/Tsukuyomi and susanoo.
Plus sasuke saw itachi form his susanoo, Yet he wasn't able to copy nor use it from the start, he had to start with the ribcage and work his way up.