It is both. They both absolutely contribute to our mental health crisis, and I'd argue it's worse in suburb-locked North America. I, as I'm sure others have as well, have identified these two individual problems as major offenders of my mental health. When I spend time away from both, I feel magnitudes of order happier. Mix that with the dystopian job culture of "the future" (today) and you've got yourself a nightmare only 80s writers would've thought of.

Lots of things changed around that time. Lots of things change all the time. Unless there's an intervention that is shown to work (ban smartphones, mental health goes up), I wouldn't trust such correlations.