I guess it's a manifestation of his spirit. The additional arms and heads themselves are probably an illusion. Though spirit manifestation alone doesn't mean it's CoC, since everyone has a spirit. But as Zoro used Asura for his last all out attack, he fueled his attack with his CoC which he awakened. Pre TS for example, Asura alone was not enough to break a pacifista, when a pacifista is fodder material for basic CoA. When Zoro awakened Ryuo the first time, he immediately cut through Daz Bones. So if Asura was advanced CoC, he would have destroyed a pacifista easily.
One Zoro gains control over his CoC, he will be able to use it with all kinds of attacks.