yeah he doesnt know but he was a coc user at that time, and later he use adv coc against kaido. adv coc is something that under top tier can pull. and clearly he wasnt top tier at the time he witness roger vs whitebeard, that was he say in his log that he was grow alot stronger during his journey.
enma and oden been hyped by oda since the beginning of wano arc, both are special. or else oda wont replace shusui with enma if it doesnt make zoro get stronger exponentially. it proven by how enma force zoro to get stronger and train hard soon after he touch enma until this very time, that shits doesnt happen with shisui, it doesnt as demanding and bothering as enma.