Noticed his funky run today too. Maybe he was surprised he was so open and there was so much space in front of him? No way he runs a 40 yard dash like that.
In my opinion it looked like he was off balance from the time he caught the ball, and he was more or less falling down the entire time. The point at which he "slows down" is finally when he caught his balance, but his momentum was already taking him to the sideline.
He may be slow, but he doesn't normally run like that.