Sion Gameplay Bug - Please Help

I just played a normal game and was dominating as Ashe bot lane. All of a sudden I hear the enemy Sion ulti and think uh oh. However, I saw him in river and decided to dodge accordingly when all of a sudden, HE TURNed ON THE DIME. I'm not sure if this is a bug or if this was a blatant cheater. The Sion could just turn every which way when he ultid, not to mention completely reverse direction!!! The player's name is Uzee. Can anyone else confirm this bug or is this guy hacking?