Yah, Pyll was on the behind bit of Rage so Pyll didn't have much choice as to where to go. If you think about it, if Pyll had jumped off then he would still be behind the falling Gyarados. When you can't move, you can still fall over by disrupting your centre of gravity. Rage tried to put some speed into it but was restricted by paralysis. You still fall faster the longer the fall though so there was some speed involved.