Folks who took the drugs took longer to play their moves. They lost more games on time, but ignoring those games, their play was better and they consequently won more games.
But imagine an alternate study where players were given the instructions to take more time on their moves. In this study, they would have lost more games on time, but when they didn't lose on time, their play would have been stronger and they consequently would have won more games.
In such an alternate study, I wouldn't say their brains got better. They just made a different choice to play at a different point on their efficient time-quality frontier.
I wonder - how much did these drugs push the frontier outward, rather than just trading off to move along it?
Nonetheless, it's interesting that this study tried to answer why/how these nootropics work (maybe they make you more reflective) and also understand in what circumstances such drugs won't help (in situations where you're under time pressure).