It just says "the reduced variance reached statistical significance in >33% of individual N-back trials comparing DLPFC stim with DLPFC sham" which I think isn't quite the same as having a statistically significant overall result. If you look at the results the sham group is better in quite a few of the graphs.

I get the impression that the study results weren't quite as impressive as they had hoped, and they have added some spin to make it look better.