The reported study doesn't deliver what the headline promises, because the study design doesn't show the direction of causation. A cross-sectional study with one date of observation of adult behavior, like this one, cannot show whether brain differences cause the sleep pattern differences, or whether the sleep pattern differences cause the brain differences. The human brain is reshaped and rewired by experience--that's what the brain is for, adapting to the environment--so it's not clear what causes what here. See the online article "Warning Signs in Experimental Design and Interpretation" by LISP hacker and Google director of research Peter Norvig[1] for more information on missing details to look for in preliminary reports on research studies.

[1] http://norvig.com/experiment-design.html