There are thousands of fuel and air combustion cycles per minute in your engine. That chemical reaction combined with copious amounts of friction make your engine a massive heat generator. Therefore, to keep it cool a radiator (a heat exchanger), filled with coolant, is used to transfer the heat away from the engine and into the environment. This means the coolant will most likely be near the temperature of the engine when it reaches the radiator, prompting warnings and hazard signs for you to never open the radiator cap when the engine is hot.
For some reason these guys thought it was alright to uncap the radiator when the engine was overheating. The next thing you know all of its coolant gushed out like a geyser, spraying what looked like boiling water.
Which brings us to another tip: Please always use premixed coolants in your car. Your car can function with water as a coolant, but you would be introducing many more issues down the road. For instance, when water freezes it expands. You run the risk of damaging your engine block in the winter time, since water has a higher freezing point than premixed coolants. Also, if you’re not careful and use regular water instead of DISTILLED water, you risk introducing minerals and impurities that will most certainly damage your coolant pump and miscellaneous components over time. So be smart and don’t cheap out on engine cooling.