It does kinda create the illusion of soapy bubble filled white water. If you change thinking about the 'white water' section to actually be the see through part in between clear round water droplets (the 'bubbles') that are clinging to the side of the container.

It's most likely someone recently poured some water out of it from the spout at the bottom and what water is left on the sides from the former water line slowly makes its way down to the new water level.