That's not a great answer. We need to know the counterfactual question of "How much would google's stock have rallied after a realistic demo was given?" I would not have been surprised if the answer was also 5%. Almost certainly Google's stock would have risen after announcing Gemini. There are other long term questions too like about how this feeds into growing dissent against Google and trust. But what the stock did is only a small part of a much bigger and far more important question.

Edit: Can someone explain the downvotes? Is there a error in my response? I'm glad to learn but I'd appreciate a bit better feedback signal so that I can do so better instead of guessing.