I got my very first smartphone last month, I've never been much of a phone person. This is to say that even before I owned one, I've always had ways to entertain and immerse myself in my own world. Especially during large commute times, I used to nap, read books and newspapers, do homeworks.. I'm pretty sure that if such thing happened to me then, I wouldn't have noticed either. This scares me a lot but the base idea, imo, is that people tend to isolate themselves during daily routine, and all assume a safe and sound environment and if such sporadic events happen, none of us really could expect them beforehand.
This is to say (tl;dr), while phoned might have amplified this effect, they are in no way the cause and the article seems to be a bit biased against them.