Earlier quoted context omitted.
You can basically say the same thing about any study that isn't a double blind randomized control trial. At some point, you need to take out Occam's razor.
I think that the problem is that for some, the obvious Occam's razor is that "smartphone is the cause. obviously" and for some "smartphone is a confounding effect of a deeper cause, obviously". Because it is like that, I would say both of these conclusions is not scientifically acceptable: the fact that some people believe that "obviously it's not the case" is enough to demonstrate that it is in reality not obvious.…
But isn't this equally admitting smartphones are the issue? Like whatever deeper cause you're talking about existed before the smartphone. Like imagine you're a farmer and you grow crops that need a lot of water and climate change causes water to dry up in your area. What you're saying is basically "climate change didn't cause your crops to fail because you weren't growing drought resistant crops. Climate change is just a confounding effect on a deeper issue."
I think what makes the discussion about smartphones unique vs. other social topics is that the adoption of the smartphone and social media was so swift that it's very easy to study mental well-being before the smartphone and after the smartphone without worrying about other changes in lifestyle.