This reminds me of a rather spectacular experiment we did in physics class.
Fill a flat bottomed flask halfway with water, and heat it on a plate till it starts boiling.
Switch off the current, boiling goes on. Put on a rubber stopper and press it on firmly. Boiling stops (almost immediately). (If the stopper is not pressed on firmly enough, it will pop off and boiling will start again).
With the stopper still on, put the flask bottoms up under a running cold water tap. Bailing starts again.
Explanation : The boiling temperature of water - or any other liquid - is related to the pressure above the water. At 1 atm, this temperature is 100°C, at 0.8 atm it is 93°C and at 1.2 atm it is 104°C. When you put on the stopper, steam is entrapped and pressure will rise so that the water does not boil any more. Under the cold water tap, steam condenses, and pressure drops so that the water can start boiling again, even if the temperature drops to 98 or even 96°C.
Here we lowered the boiling temperature by decreasing the pressure, with your pressure cooker you lowered the temperature in order to decrease the pressure.