When you put sparkling water in the freezer to cool it quickly, you exposed it to very low temperatures, which caused the carbon dioxide (CO2) gas, responsible for the carbonation and fizz in the water, to dissolve more readily into the liquid. This is due to the solubility of gases in liquids being temperature-dependent; gases dissolve more easily in colder liquids.
When you opened the cap after an hour, the sudden change in pressure and temperature caused the dissolved CO2 to come out of the solution rapidly. However, since the gas had already dissipated while in the freezer, there was no carbonation left in the water, and as a result, you experienced no fizz or bubbles when opening the cap.
This phenomenon is similar to what happens when you shake a carbonated beverage and then open it, causing the release of dissolved CO2 in the form of bubbles and fizz. In your case, the CO2 was already lost due to the freezing process, so there was nothing left to create the carbonation effect.
If you want to cool sparkling water quickly without losing its carbonation, it's best to use a different cooling method, such as placing the water in an ice bath or refrigerator, where the temperature remains above freezing and won't affect the dissolved CO2 as much.