Oh there's no doubt in my mind that the dolphin was aware that he needed help and deliberately sought it out among humans. Not only did he approach a nearby diver and present himself with the hook plainly visible, he made adjustments during the assistance to help maintain position... AND... after leaving to surface and get some air, he returned BACK to the SAME HUMAN, patiently allowing the process to continue until freed. Once the dolphin felt the hook was gone, he happily swam away!
This clearly shows sentience. A typical wild animal would be caught up in the discomfort and not know what to do, perhaps even going berserk in the process. This dolphin was also thoughtful... he could have easily swam to another nearby human after having surfaced for air, because there were several divers nearby. But it returned to the same diver.
Unfortunately the article was sparse on information. I wonder if the dolphin made any kind of "thank you" gesture to the human who helped him.