From what I understand, is unless they stop the play live, they cannot review whether or not the clock started on time.
So when they went to the review, they were only checking to see if he got the shot off before the clock expired (which he obviously did) and if it was a 3-pter (no foot on the line.)
I could be wrong on that, but I'm fairly certain they can't review whether or not the clock started correctly, unless they stop the play live. It's a situation that needs to be able to be reviewed, as the "home-court clock" is always going to be part of the game unless the NBA starts putting an official at the scorers table.