Constant conjunction is not causality. What type of people are most likely to buy an iPhone? If you say liberal affluent professionals, well, there you go.
They are implying all “smartphones”...so Android users affected too supposedly (their paper is still in the “working” stage and has zero tech facts so far). As you mentioned “conjunction is not causality”. I think they are going for a “screen time” type thing rather than a “RF emission” type thing. They are speculating like anyone can do...maybe it is the rise of streaming video services? Or the rise of video games? Or the rise of ?