Bears are very social mammals, usually they have share light instants with human. But animal is animal and beast is beast. It might be unexpected change in their nature. They can forcefulness on human anytime. No matter how numerous light instants you have co-operative with any of the animals.
Equal thing occurred with the person in video. He was teacher of bear and it was training session going on when rapidly bear attacked on his bear, but cheers there was two more persons to assistance in this situation. It was exercise session when one of the trainers went fast and stood organised with of bear.
Bear was stand-up still and coach too stood quiet and trainer was trying to copy the erect chic of bear. It was blink of eye when bear rapidly attacked on its trainer. It was terrifying instant for other people standing nearby bear.