@481ece9a Your interpretation is possible, but it does not mean it is correct; note that one of the most robust results in happiness research is that religious folks are more happy. The possible interpretations are that either deep religious beliefs provide a framework which gives your life meaning; OR that religious people are less educated, more conservative and hence they are ashamed to report mental health reports; or we could create more ad-hoc explanations. In similar manner you could explain away every such finding. 

Similarly, you could argue that scales 0-10 are incomparable across the cultures; that questionnaire-based survey like this are inherently subjective and hence invalid; that sample based on adolescents is wrong, since 15years old in Poland and in India might be on different development stage.

But still, I would say that in that in this particular report the findings are reported accurately. Maybe I should be more careful in quoting, giving caveats that this is conclusion related to this particular dataset only and one should be careful before trying to generalize it.