All this proves is that Nadal is a hellish matchup for Fed. Fed playing on the grass side means better movement, but Nadal's shots end up coming pretty quickly at him, there's not much advantage there. Nadal is on his clay side which means he has infinitely better movement and shots come to him in slow motion, and he's able to run around his BH to dictate play with his FH.
Hmm, roles reversed... would this now give Federer an advantage if his opponent was playing on a grass instead? Nadal would have worse movement yes, and balls would be coming at him quickly. But then again Fed's movement has declined as they switched sides. And Nadal when he gets a chance is able to hit that high bouncing forehand to his Fed's OHBH which bounces up high and probably comes back weak allowing Nadal to dictate. Also don't forget this is 2007 where Nadal's level was pretty high on grass as after all he made 3 Wimbledon finals in 3 years.
Moral of the story is, Nadal's clay prowess far exceeds Federer's grass prowess at the time. Nadal was almost unbeatable on the damn surface back then, and was a pretty good grass player. So basically this matchup disadvantage heavily favors Nadal no matter what as Federer's advantage on grass over clay is not higher than Nadal's advantage on clay over grass. Nadaltards exposed.