Kaido assumes that Zoro used CoC because the only guy who left a scar on him before used it.
But, as mentioned, Kaido is asking if Zoro used CoC and Zoro denies it. Zoro's power was simply that good.
It was expected that Zoro's ultimate does something more than a mere Tatsumaki.
We see 2 Klang SFX and their appropriate clash marks, which dont appear on a no-touch CoC barrier.