digging a bit more in the MFnMesh class I am trying to access the vertex normal.
In the image you can see two blue lines that correspond to the vertex normal obtained by the getVertexNormal() method. One is with the angleWeighted arg True and the other False, but that is not the issue. What I find odd is that to check that any of those vectors correspond to the vertex normal, I displayed in the viewport the normals per vertex, and neither of the normal vectors I obtained correspond with the one displayed.
Any idea why? my guess would be that the viewport is not as accurate to improve performance and that the correct values are the ones provided by the method but it is just a speculating.