Azir's auto-attack glitches

I was playing a game with Azir last night and while he was auto-attacking he randomly swung his staff back and forth frantically for about 1.5 seconds. The person I was in the lane with noticed him do it as well. I thought it was just a momentary thing but, about five minutes later he did it a second time as he was attacking a turret. I only encountered it those two times but, I thought it was worth mentioning.