I have a few doubts on this. I'm not sure whether I'm misunderstanding the article.
It sounds like they haven't actually monitored anyone's sleep. They've used a big DNA data bank to identify people who have genes that are related to napping, and then found that the same people have statistically larger brains.
Nothing wrong with that, but then they go on to conclude that napping causes bigger brains?
That sounds like a bad attempt to imply causation from mere correlation. What if bigger brains cause naps?
Also, they say they do this to get rid of confounding factors, but what if they are getting rid of the actual causation instead? I.e., what if nap genes cause bigger brains even in people who don't actually nap? I mean, you already know that those genes have a neurological effect; isn't that an easier explanation?
And that's without even getting into brain size alone being a poor proxy variable for, well, anything.
Basically, I really see no reason to suggest taking naps for brain health. We'll need more and different studies before we can say that.