I've wondered the same. Concluded that as the powder is reconstituted before drinking, it's a liquid and can be considered juice -- though it's not of the same nutritional content compared to very fresh juice. What do you think?
Nowadays we have all sorts of super green foods. Have to make sure of what other ingredients - fiber and fillers -- are added, that's a thought.
I do remember that the first juicing regimen for illnesses I heard of used fresh carrot juice daily, but also included daily doses of barley green powder. (Barley greens powder was touted at the time, as I remember my friend who was using this diet to recover from cancer, as one of the only -- the first? -- spray freeze or vacuum ?? dried dehydrated greens that I knew of at the time, maybe the only one, and extremely nutritious.. I don't have any verification of that -- it was pre-internet pretty much. )