That's a mischaracterization of the study. The very next sentence:

  However, the standard deviations indicate that there is considerable variation in how students allocate their time to these activities.

Additionally, their data is an "analytical sample" extracted via "weighted random selection" from a larger data set from more than 10 years ago. We don't know how well that sample fit the broader reality a decade ago, let alone today.

That you went fishing for research to support your argument and this is the best you could find is telling.