Whatever the cause of this mysterious belief system, please know that rivers, like all other objects on earth, flow downhill due to gravity. No matter where the river, it will take the path of least resistance and flow downhill as rapidly as possible. Sometimes, this path is south and, just as likely can be north, east, or west, or any combination of the directions of the compass.
I enjoy this analogy - would you go to Seattle, Washington and rent a car and then let it coast to Los Angeles because Los Angeles is south (and thus downhill) of Seattle? No! Just because Los Angeles is south of Seattle and thus typically displayed "below" Seattle, it does not mean that south is downhill.
There are countless examples of rivers flowing northward. Some of the most famous rivers that flow north include the world's longest Nile River, Russia's Ob, Lena, and Yenisey Rivers, the Red River in the United States and Canada, Canada's Mackenzie River, and California's San Joaquin River.
There are dozens, if not hundreds, of additional rivers and streams that flow northward around the world.
Therefore, know that rivers often flow north and that rivers only flow downhill!