Ok, I can understand that. It can be dificult to judge an octopus' true size, especially in a video. That little clip of the video does not state the actual size of the octopus but I remember that it was at least 8 FT long (probably longer) it says clearly in the video that the sharks were 3-4 ft long. Note how it is able to envelop the shark, that is one indication of its true size. Here is a pic that will help you to see how truly massive this octopus is:
even if they were evenly sized, my money would go on the octopus:
Sharks only weapon is the mouth plus they have highly developed senses, and while I don't think that sharks are as dumb as most people think they are, they aren't geniuses either.
Octopi have eight powerful arms covered in suckers, a mouth that is every bit as dangerous as a sharks, plus they are very intelligent.
Oh, BTW, don't get me wrong, it is a cool video, it is just not surprising to me.