How is fermented tea “mushroom water”?

Old coworkers used to call the growth mushroom as slang for some reason, at least that was the first thing that came to mind.

The other one is a ludicrously overpriced relatively recent beverage called mud water (caffeinated mushroom water?)

In Russian, it is called grib, aka mushroom

Some call the mother colony a 'mushroom'.

I've never heard Kombucha referred to as mushroom water. I assumed they meant Chaga.

Mildew. It tastes like mildew.