Looking at the rulings of Riot Control on gatherer and it states that the player who is being dealt non combat damage gets to choose to prevent the damage before can be redirected to Planeswalkers.

However I was under the inpression that the prevention and redirection was being applied to the damage source meaning the controller of it gets to choose the order to apply them in. Do I have this wrong?

The ruling on Gatherer is correct.

When two replacement effects (prevention is replacement) compete to replace the same event, the affected player or the controller of the affected object gets to choose which one to apply first. In this case, the affected player is the recipient of the damage.

Daniel Kitachewsky
L3, Paris, France
Rules NetRep