Well, the time Steve Ballmer announced he was to quit the Microsoft, Microsoft's stock jumped quite a bit, clearly because Ballmer quit, even though one could perhaps explain either a raise or a fall with Ballmer quitting. Expected square of a change was big from Ballmer quitting, that's for sure. Same goes for any dramatic news, such as the recent gas attack in Syria.

And yes, over the time one could tell that something is up if the stock market graph is uneventful while there's dramatic news.

Bottom line is, a causal link can exist and be inferred even when there is no correlation.