The experiments were conducted on mice so probably have little applicability to humans. For what it's worth, the experiment used mice housed in cages with access to a running wheel for 30 days of voluntary excessive. The control group did not have running wheels.

As the husband of a neuroscience researcher who works with a mouse model, I believe you'd be surprised at the applicability of such research towards human analogues.

What did the other mice do? Just sit around, doing nothing?

Can't comment on this one in particular, but the threshold most often set forth for this or that health benefit from exercise is 30 minutes of elevated heart rate a day, aka 3-5 hours a week.