I appear to be in the minority, but after looking at the video and listening to the description/discussion between the floor persons, I agree with the decision of the floor. He definitely starting his betting action by moving 3 stacks. Granted the 3rd stack did not move very far, but it did move forward before it "dropped" off his thumb. I agree with the decision that his is not a string bet.
In my opinion the whole thing depends upon whether he started the original action by moving 2 or 3 stacks. It is clear to me that the 3rd stack moved forward, albeit only a little. Had that 3rd stack not moved, I would then rule it a string bet, but move it did.
Chet
Added the following:
Personally, I would like to see a rule requiring all raises to be verbally declared including the total amount of the bet. However, I am not real sure this is a practical rule. What do you do if the players do not speak the language of the event? I know that if I were to attend an event in most all of Europe/Asia/etc., I would be at a disadvantage because I am one of those "English Only" folks. So I think we can propose all kinds of rules to resolve a multitude of problems, but they may not be practical in the "real world".