In the latest chapter, we learn that there is a type of Armament Haki that is very similar to the technique Zoro taught himself during his fight against Mr 1.
However, what if that same technique is also related to the prior form of Armament Haki, the invisible Armament Haki we had seen during Marineford?
What if the “Steel cutting technique” is simply just the invisible coat of Armament Haki applied to your sword. We all knew Zoro was a strong swordsman, even before timeskip.
But it’s quite obvious Zoro got a powerup during/after Alabasta. So what I am saying is Zoro might of been using invisible Haki on his sword the entire time since Alabasta. Even he himself wouldn’t of known it was Haki at the time.
The scene where Zoro cuts Kuma with Shishi Sonson also makes sense. We all agree Kuma is pretty high tier, and for a low tier such as Zoro pre-timeskip to be able to cut Kuma, you would really need Haki.
How it is related to the deflection ability shown by Rayleigh and Sentomaru, is still to be revealed. But its possible the two are related.
But Hyougoro mentioned, when he was trying to figure out what Luffy was talking about, was the same ability Zoro learned in Alabasta is what Wanokuni outsiders call “Haki”.
It’s possible the way Oda is going with this reveal is that there are two types of Armament Haki. It’s possible that the invisible Armament Haki might be less durable, but have other benefits such as being able to use these deflection impacts. This also explains why Zoro was all of a sudden able to cut through steel.
Applying Haki to his blade, he overcame steels durability. The “cut nothing” part of his masters lesson would refer to the calmness required to use this invisible Haki.
*Theory by Visoth