To be honest, I’m skeptical about the work in a couple of ways.
First, as some others already pointed out, correlation does not necessarily
Second, I’m not sure if it is more accurate (in predicting) than existing quantitative measurement of market calmness (or the lack of it) such VIX , or put/call ratio for an individual stock. While I don’t have any statistics, I personally find put/call ratio of GOOG is usually more informative (and direct) than reading tweets about $GOOG. Of course, their work is about the market as a whole, which I have no clue. Why their result is for 2-6 days later,
but not the next day?