I think what you're talking about is some sort of a dried and pulverized sweet tea (looks like little green pellets?) If that's the case, I've had it: my sister-in-law is Japanese, and sometimes she brings unorthodox teas from her visits home

Indeed, it dissolves in water--the one I had was sweetened. I wasn't a huge fan of it--it didn't taste like tea, had cloudy appearance, and made me curious of its origins (which I assumed to be a laboratory)... By the time we got around to trying it, my SIL wasn't around to translate what was on the package, so I don't have any details. Of course, we might be talking about totally different teas
Btw, kombucha is a type of microorganism formation that thrives on sweet tea. In order to make kombucha tea you must obtain the starter (some call it "mother")--a rubber-like slippery substance. I'm pretty sure that's not what your friend picked up
Do share your experience with it, and post some pics!!!