> No discussion as to any other effect of screen use.
That's not what the study is about. The study was about a particular effect, and they published their conclusions. The need for such a study can be debated but there is a difference between "common sense" and a proper peer-reviewed study. And to be published by what looks like a serious journal, I guess it wasn't so obvious to experts.
I am fed up with articles that proves a controversial point and then the reporter has to add a "but...". Maybe useful on prime time TV, so that people who are unfamiliar with scientific work don't get the wrong idea, but this is a university, and people reading this are supposed to be familiar with the scientific process.
Maybe some other group will later use the results of all these study and say something like "even though kids with more screen time are better at video games[citation], there is no significant improvement in related activities, we also noticed a decrease in...". But that's another study.