By the letter of the rule, it was legal. Catcher had to move to where he was to catch the ball, and prior to catching the ball, the runner did have a path to the plate (his foot was sort of in the path, but ...). As soon as Sanchez had possession of the ball he can move Into the base runners path if he chooses(which he did). At that point the runner is within his rights to run him over if he wants to.
If Sanchez had decided to stay where he was when he caught the ball, the runner would have to avoid contact and slide in to home or just run across.