After some discussion with his mother, who was also there, it was revealed that the kid had mixed in his mom's leftover colonoscopy prep stuff into his smoothie, seeing only that it was lemon flavored, and thinking it was some sort of protein powder. Fortunately, there was TP on hand for the emergency dive behind a tree.
On a similar note, I just started drinking the stuff myself for my procedure in the morning, which is when my wife reminded me of the incident in question.