Yes it's obvious & if people Read well, he used it against Kaku too
Zoro not being able to Cut Kaku at first wasn't because of his Tankiness, it was because of his Tekkai & how he switches Fast
So when Zoro chooses to Cut Flesh, Kaku activates Tekkai but when Zoro attacked with "Shishi Sonson" to Cut Iron, Kaku disabled Tekkai & Survived. But Asura was able to Defeat Kaku regardless of whether he is using Tekkai or not meaning it was definitely an Internal Attack that ignores outside Material
Asura is definitely Advanced CoC & that is why Oda made Zoro oblivious of it.
Because if it was just CoC then no need to tease it more, just make Zoro admit he is CoC User since you're giving Luffy Advanced CoC so it won't hurt his Captain's Portrayal but since Oda made it Unknown means he wants to Hype Luffy first & tease for us that Zoro is next
Zoro will most probably ask Luffy about it at End of Arc or just Practice it by himself & decide to use Asura more often & not only rely on it when he is Heavily Injured