pybind11: return c++ class (with an existing python binding) to python

I am trying to create a wrapper for a c++ method that returns a c++ class(vtkPolyData) which comes from an external c++ library (vtk). The same library has python binding available which is already installed in my python environment. How do you tell pybind that the c++ class (vtkPolydata) and its python variant are the same?

I tried to use this custom type caster macro. but I get TypeError: Unable to convert function return value to a Python type! The signature was : (self: Versa3dLib.skeletonizer, offset distance: float) -> vtkPolyData

which is confusing since it looks like the conversion maps to the correct type but python is unable to interpret it. So I am not sure what's wrong since I don't see anything wrong with the macro either. I noticed that in python vtkPolyData has type vtkCommonDataModelPython.vtkPolyData. is that why the conversion is not done correctly?