Well, I just took a closer look at it by running it through slo mo on my dvr.
The ref definitely didn't blow the whistle on the Marquis foul until Marvin Williams had already let go of the ball, so the right call was indeed made. Horford shouldn't have gone to the foul line for 2 free throws there.
Also, you have the rule wrong. The deliberate aspect of the rule you are referring to only applies to a situation in which there is an actual area of offensive action. There was none on that specific play. It was an inbound attempt. Offensive action doesn't start until the ball is inbounded, and, as such, whether the player was deliberate or not is irrelevant when we are discussing a throw in attempt.
The only part of the rule that can possibly apply is if the ref determines that a player is fouled before the throw in ever occurs, regardless of whether or not the foul is deliberate. If the ref determines what a player did to be a foul, doesn't need to be deliberate, then the player who is fouled will be getting 2 free throws. I re-watched it for myself just now, and I'm happy to say that that is not what happened. The ref blew his whistle immediately after marvin threw the ball, not before. I'm really happy about this, because I really thought we benefited from a bad call last night, but it seems the refs indeed made the right call.