This is fascinating.
That said, if it's possible to do better than random guessing, then does this reflect the fact that the five charts are presumably hand-selected to be "interesting"?
My naive guess, and I'd be very curious to learn if this were wrong, is that something very close to the efficient market hypothesis is true; that, if it were possible to beat the monkeys on randomly chosen stocks on random dates, then someone would have figured this out already and deployed bots to capture whatever profits are available.
They're from a seeded random draw. Random S&P 500 stock, random 60-day window that's at least 12 months old, every player gets identical charts. Gemini writes the narrative vignette.
Your instinct is pretty spot on. 6,000+ calls in: players state ~74% average confidence but hit ~54%, and accuracy is basically flat across confidence brackets. Up only strategy quietly beats the coin flipping monkeys but players call down 43% of the time.
The interesting answer by the author, will_asouka, has been marked 'dead' for some inscrutable reason.