Tap water has been cold and under pressure, so it will have lots of gases dissolved in it, both CO2 and O2. When you add it to your tank it is warmer, and not under pressure, so the gases come out of solution, making little bubbles everywhere. That isn't pearling you see, just the dissolved gases in the water escaping.
You can get pearling from a water change because of the added CO2 and O2 in the water, until it is used up or escapes. That will look about the same, but will all be from leaves, instead of being everywhere in the tank. It goes away soon because the CO2 gets used up or escapes pretty quickly.