Cocoon... mesh? or nurbs?

I just found something interesting.

When I bake a Cocoon only, it makes a mesh components and can only be saved as stl file, and it cannot be saved as igs file directly. So, I tried to use "MeshtoNurbs" in rhino and it took so long that I forced to stop it.

However, if I add a component Cocoon Refine, then it makes a nurbs-based part, and can be saved as an igs file directly.

How can this be possible? In a very short time, the Cocoon Refine executes "MeshtoNurbs" !!