Of course there's some knowledge about that, but the approach in the link identifies the pitch by an NN (this step is not relevant to the current discussion) an

Of course there's some knowledge about that, but the approach in the link identifies the pitch by an NN (this step is not relevant to the current discussion) and then applies an FFT based method for pitch shifting that doesn't take any of it into account. So it'll shift formants as well, making voices and instruments change their character substantially.