Pearling means bubbles of gas sitting on the surface of the plant.

In this case, it refers to a situation when the water is saturated with
oxygen and the additional oxygen produced by the plants does not
dissolve in the water anymore. Then, you can see the bubbles of oxygen
sitting on the plant.

But if you get this in the first two days of water change, this is more
likely to be all the gas dissolved in your tap water.

I'm not an expert at this so correct me if I'm wrong.