Correlation, meet causation.
What is different between teenagers using social media and those who don't (I suppose other than the other group living in some Himalayan valley without Internet)? Do parents spend more time with less terminally online teens? Do they engage in high-engagement hobbies (like horseriding, or electronics) that are fulfilling, though maybe costly (which would make that approach less available to the majority)?
If you control for these things, I am fairly sure you will find that kids with a higher involvement of their families in their lives are more happy on average.
As long as you do not put two random teenagers in a concrete cell each, controlling for all outside parameters, and show me that the one without the cell phone and social media is happier than the one with those things after a week, I will remain sceptical.