Luffy first trained to do the haki barrier thing in udon, then in his fight with kaidou learned how to do IT not just with coa but coc too.
Zoro without that haki training, or even knowing that he has coc got Enma that basically skips all that haki training nu having IT absorb all the haki from Zoro, including coc, basically imbuing his sword with coc without knowing he did IT and removing the need of advanced haki training. So Like a Cheat code, i Guess.