I don't think it has anything to do with screens per se - it's about being alone and free to think, while not being able to do anything else. Other people are as much, if not more, distracting than screens - hence the time spent in shower or on the toilet is so frequently mentioned as the source of valuable insights.

A guy I work with showers with his Galaxy S8, or at least that's what he said he does.

It was true before smartphones came onto the scene.