While a control group is essential to determine if the effect is really due to the treatment or to practice, if they did the mouse study first and expected a positive effect, then they might have felt pressure to only have a human treatment group in what looks like a pilot trial. Maybe their original proposal included a control group, but their institutional review board decided against it?

I'm a little surprised they wouldn't have done a larger secondary trial before publishing, the impact would have been much greater if the effect was still observed in a larger group, even if they still did not have a control group- or perhaps had an alternative treatment schedule (shorter exposure times- is treatment duration correlated with degree of improvement? Then you have less of a moral dilemma of denying participants of a useful treatment while still getting some data that would indicate the treatment itself actually does something).

(working on a PhD in genetics)