Kaido has probably seen another user of CoC that has a similar techinique like Zoro, maybe Shanks can make an arm using CoC or something, that's why he recognized. It's the embodiment of the user's will, that's what Zoro does, i guess there's other ways in wich to use CoC.
Isn't that a good thing? Luffy gets two applications of the CoC and Zoro gets a different one, sounds perfect to me.