Purgatori Onigiri is a close range attack.
It became a range attack after Zoro added ACoC to it.
Zoro knew flying slashes and flowing CoA haki prior to Wano.
You don't understand the sequence of the events. It goes like this:
- King attacked Zoro in mid air
- Zoro blocked King's attack
- King changed his sword to sword catcher to try to take Zoro's swords
- Zoro released ACoC from his body or used no touch ACoC to blow King away from his swords and himself
Yes they are different. CoA can be used externally or internally. The following scene explains that.
Zoro uses barrier CoA haki externally to cut cut Kaido. Luffy uses internal destruction CoA to by pass Kaido's scale and damage him internally.
Go back and read my post. I said the skills used to flow CoA haki can be applied to CoC. That's how Luffy and Zoro learned ACoC so quickly. That's why Luffy remembered his flowing CoA haki training with Hyou prior to using ACoC. You can use both techniques at the same time or separately.