The most distinct thing I can remember about gaining Infini-fly with TonTon was what happened right before it. The frame rate on the PS3 version of the game dropped exponentially to where I thought my game was actually going to crash. I've tried to reproduce it around the end of the level where you can sink below the sand, your wayfarer turns black, and its head thrashes around along with the scarf, but I've never been able to gain the ability again. If I remember correctly, Tonton's and my connection hated each other and we weren't able to coast very well as a result.
I'm not sure if something similar is happening to those who let the game sit for a while, but sudden framerate drops could be one factor into reproducing the glitch.
It's really neat to see that it's been happening to other people though, even if it is ultra rare.