Unless its stated explicitly in next chapters, Kuzan doesnt have CoC. Oda always gives us statements when someone has CoC. He has no reason to hide that when it comes to Kuzan, we all know Kuzan is super strong.
CoC strikes can touch, thats not the issue here. The biggest issue is he doesnt have any trails when he initiated the attack =>
Could Oda hide Kuzan emitting CoC trails when he hardened his fist? Its not impossible, but it sounds ridiculous to me. Oda doesnt need to go to such an extent to hide Kuzan's CoC.