That study is exceptionally flawed and should be taken with a grain of sugar. It has not been peer reviewed, been poorly examined, and if you look at the figures, I think it was just over 4% of the 260k odd number of participants were shown to be depressed. The national average I believe is something like 6.7%. Therefore, the group had a lower number of depressed than if you were looking at the general population. Conclusions to be drawn, none.
I do note they missed all that info about the national average out of the article.