I watched the video about six times, and by the sequence it appears that the actions of the dolphins had an effect on the outcome, but there are two big questions.
The first is "was te shark intent on biting...hence using the term "attack". The shark does approach from beneath, but if you look closely at the video the shark is about two feet from the diver's fin before turning and its mouth is not opening. Now we all know, or shold, that a sharks vision is it worst sense. It looks very much like this is just a "cursory look and pass" rather than an all out attack. I base this not on seeing sharks in the wild (yet) but by being an admitted nature channel adict and spending many hours watching shark video (not the hollywood crap). I could be wrong though.
The second question is did the dolphins give a crap about the human, or was the alpha of the pod (there were 5 of them so I'm not certain if this qualifies as a pod) merely trying to protect his/her pod and the human merely, through tremendous luck, got the benefit of the pod's proximity?
Things that make you go HMMMM.