Because technical incompetents (these days mostly non-sentient software) playing the stock market are the final word in the validity and future potential of a new technology.
Not really. Stock prices react to "news" quite consistently - earnings reports usually have the most dramatic effect, but everything significant from corporations will move the stock price. Compare the Apple announcements (even the widespread "rumors" of forthcoming announcements) to the movement of AAPL. Amazing what millions of people can do with a widespread meme, even when it's just a mass hallucination.
The fact that the stock continued to drop after this announcement basically says "it's nothing". Or, it's nothing they're going to make money from. But we already knew that.