Two angles: "This video was shot at San Carlos Beach in Monterey, CA - aka "the Breakwater".
A few guys were doing a night dive, and they were joined by Whiskers, a local harbor seal who often accompanies divers at night to hunt with their lights. They saw him earlier in the dive, but by the time one of the divers found the octopus, they hadn't seen him in a while and figured he left to go hunt elsewhere. He was entirely out of their mind when he swooped in and ate the octopus, so they were completely surprised. You can hear one of the divers laughing in the background after the chomp.