Supercooled water is kind of a cool phenomenon (pun not intended), but you can reproduce this trick in your freezer.
When water is cooled below 32°F (0°C) the water begins to form ice crystals along any foreign particles or bubbles or other ice crystals. If the water is so pure and the container is so smooth smooth that there is nothing for an ice crystal to form around then you get super-chilled water. There is nothing for an ice crystal to "hang on to" so it doesn't form. The instant there is something for a crystal to form around the entire bottle will turn to solid ice. When the guy smacks the bottle, he is creating bubbles where crystals can form and sets off the chain reaction.
The same thing happens with super-heated water at or above 212°F (100°C). The old story about the exploding cup of water in the microwave oven where the water appears to be just hot until it is disturbed them instantly boils the moment it is disturbed happens due to the same physical phenomenon. It is the impurity in the water that allows the water to boil.