The discussion of the results leaves much to be desired. The nature of the task is highly synchronized, so it's not surprising to see "brain wave" synchronization that correlates with higher performance. The task also involves auditory signals and timing, which may influence the identified brain regions and activity.
I would like to see this independently verified, and validated across tasks that are primarily visual or proprioceptive. It would also be especially instructive to contrast this to the sense of flow state achieved in high-level competitive play, such as technical fighting games.
The inclusion of line numbers in the paper and the separation of relevant text from graphics is an effective way to disrupt flow of reading the paper. It's a shame I wasn't hooked up to an EEG.