Watching in full speed, it was questionable, and the referee erred on the side of caution. We can't tell what the referee actually saw from his vantage point, so it is hard to tell. Watching the replay, it looks like a perfectly timed hit. These kinds of hits are always going to depend on the vantage point of the official. If the referee was one or two steps to his left or right, the call could have been a clean hit.