we have seen that coc imbued attack have black lightening before even attacking, maybe there was a normal coc burst from zoro(like that of luffy in marineford) because he is in critical condition, or kaido mistook it for something else
anyways kaido is wondering whether it is coc or not and zoro who trained with WSS doesnt even know whether it is coc.
zoro has coc everyone knows that, but asura wasnt coc imbued attack