probably went all Bear Grylls and drank his pee.
There are snow fields in his video, he camped rather low that one night in a valley that looked pretty darn green, and it seems this was very early in the season. He also moves mega miles a day, so he probably did ok carrying a gallon or so.
I've seen some of his other videos going off trail in the Sierra just on a whim, not knowing where he was heading. Rather sketchy at times, and he clearly lacks the kind of "what if" concern that keeps people like me from trying things I haven't researched to the t.