The shockwaves come from his sword, it’s easy to assume he can channel haki through it
also Haki is the most vague power ever, Oda can come up with multiple haki abilities with adCoC and no one would care
That's what I'm trying to say. They can use Haki like Whitebeard did.
Whitebeard Projected his Haki Ryou to materialise Logia user like Akainu and then hit him with Gura punch.
Law can Radiate haki like that too given How he worked against DoC q Hax. And then land his puncture Wille.
Or else on logia it would have no effect.
Only problem is Haki is just a medium for Types of WB , Bigmom, Law , Fujitora to land their DF attacks.
Unlike Luffy Katakuri Doffy , where there AP is enhanced with Haki. Gear 4 , Holy bullets , Power Mochi.