I haven't re-watched it, but am assuming the refs think he picked up his pivot foot before he goes to dribble - I didn't think anything of it until the refs made the call; I always just assume they are picking on Kelly.
With the traveling that is accepted in today's game, I find it strange they chose to emphasize this. I mean, Lebron goes from behind the three-point line to the hoop without dribbling on nearly every drive.