Assuming the news gets printed before market open (not really a safe assumption in the digital age), for this to have predictive power one would have to be look

Assuming the news gets printed before market open (not really a safe assumption in the digital age), for this to have predictive power one would have to be looking at the intraday difference from market open to close, or the difference from previous close to today's open, not from previous close to today's close. It's not clear from the abstract/article which they looked at.