Reading the details, we learn that two tasks were imposed on the subjects during the experimental period. Before a brain scan in the morning, they spent some part of the preceding evening reading a section of a novel; then, immediately before the scan, they were quizzed about their comprehension of the novel and how it was affecting them.
The authors admit in the Discussion that being quizzed could have caused the changes in the brain scan. But they conclude that it didn't, and that novel reading was the actual cause, because reasons. "Being questioned creates changes in your brain" did not make such a good press release.
Maggiekb is right about picking out the main lesson here; that 'resting brain state' is not a kind of neutral reference point, an Absolute Zero of neural nirvana.