"TH-THAT WAS CLOSE...!! HE WAS AIMING RIGHT FOR MY HEART...!! BUT!! HE WASN'T INFUSING IT WITH CONQUEROR'S HAKI...!! WHY NOT...!?"
Sommers is terrified and says:
"HE DEFINITELY USED IT EARLIER...!! DON'T TELL ME THIS GUY... CAN'T CONTROL HIS 'COLOR OF THE SUPREME KING' YET!? THAT MUST BE IT!! WHAT A WASTE OF TALENT, YOU IDIOT!!! BUT WAIT!! HE DID CUT THROUGH THE THORNS...!!!"
This statement pretty much shows that until this chapter, Zoro's use of adcoc was random. Sometimes he could coat his swords with it(end of fight with Kaido or King, or when he first clashed with Sommer's Gram), but sometimes he couldn't, all that without even knowing
So this chapter served to allow him to do this at will