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Any character like Tashigi, Grus, Helmeppo and even fodder characters from the marines or pirates could have commented on it being CoC but nobody did.
As for those panels you presented, literally in every page where ACoC was used there's the giant Haki trails I mentioned.
Coby attack doesn't have those and looks more similar to that old dude that taught Luffy AcoA. It being a large scale attack doesn't change things. Take for example Sanji; his attacks are usually small in scale but when needed to those same attacks could be large in scale case in point the two cases of Hell Memories against Wadatsumi and Queen.
As for those panels you presented, literally in every page where ACoC was used there's the giant Haki trails I mentioned.
Coby attack doesn't have those and looks more similar to that old dude that taught Luffy AcoA. It being a large scale attack doesn't change things. Take for example Sanji; his attacks are usually small in scale but when needed to those same attacks could be large in scale case in point the two cases of Hell Memories against Wadatsumi and Queen.
Luffy only at chapter 1010 reallized Kaido was using CoC on his attacks. He had no idea before.
Coby attack has nothing to do with Hyogoro attack. In fact Luffy's CoC coating attacks is more similar to it.