The command first computes a center of gravity and then the inertia matrix at this new point. In the next step, eigenvalues and eigenvectors of this matrix are computed. The eigenvectors describe the basis of the mean axis of the affine sub-space, generated by the set of input points.
Thus, the returned origin is the center of gravity and the returned vectors are the eigenvectors of the inertia matrix from which a mean plane is computed.