Clock skew in that the clocks used by the participant may or may not have been synchronized. There are, effectively, no details about how the timing is done on the news side and there is allusion to some use of EDGAR posting timestamps which are from an entirely different clock.

Even more concerning, is that they map news events to market data using non-synchronized market data timestamps. It appears to be TAQ data. The timing aspect of the entire article is very poorly described but yet is fundamental to the claim they are making.