The study doesn't claim causation. Instead of mobile device use causing executive dysfunction, it is more probable that the correlation is because mobile device use is more effective at calming down a child with poor executive function than a child with typical executive function. That's not to say it's a good way of calming of course.

Alas, you've received downvotes even though the substance of what you say is valid.

I'll say it's misguided, as well as the root comment to which you're reaponding. The particular study soesnmt show causation, but there's a growing bidy of research that does (it's easy to find).