True, but he never really made a move to go to third. He stood next to the base, but he happened to be standing on the third base side of the base and the umpire, or more specifically the replay umpires because the guy on the field was staring right at the play and didn't make the call, decided that standing on the third base side of the base meant that he had made a move to go to third.
My problem with the umpiring on the play is that the replay umpire substituted his opinion, that Cruz made an attempt to go to third, for the game umpire's opinion, that he did not make an attempt to go to third. And replay umpires aren't supposed to do that.
My problem with the play in general is that I'm not sure why you would stand where Cruz was standing, even if you knew it was allowed. Just put your foot on the base and keep it there. If the ball isn't caught you can go straight to third. If the ball is caught you can run back to first. No retouching the base necessary, because you are on the base at the critical moment.