Don't know never heard that fact, especially considering that rivers that flow north in Europe are quite common since the norther part of Europe is still rebounding from the last large ice age and it's overall at a lower elevation than southern Europe where you also get the large mountain ranges.
So famous rivers like the Sine, Elbe, Oder etc. all flow "north".
So famous rivers like the Sine, Elbe, Oder etc. all flow "north".