Does the model render as a smooth surface with a different material on it? Right now it looks faceted as if it is "flat shaded" instead of smooth shaded, which points to an issue with the normals set up. If that is indeed the case, the curvature node is just calculating the angle difference between the facets, rather than the "normal" curvature of the surface as a whole because the normals are not set up properly.
If it does render smooth with other materials, then I'm not sure what the issue would be.