Non-investor, and I was conflating too many concepts, but, very roughly: based on fundamental value of the business vs. only how others will react in buying&selling of the stock (and maybe even nudging others to react).
In any event, this sort of news generally does not move the fundamental value of the business in a way that exceeds the "uncertainty band", so pretty much all of the active trading is necessarily in anticipation of how others will view the news.
This is in contrast to e.g. merger offers, which are much more about the actual value of the business (which has suddenly become very concrete and precise), and not trying to judge the reaction of others. But major events like that are a small minority.