If they are talking about tablets and laptops, exclusively, they ought to state that and limit their observations to what they observe. As it is presented, the study is naive.
Too bad, too, because as several of you pointed out above, there is a germ of a useful insight: people can read best when it's presented in the manner they are accustomed to. I configure my Kobo Aura HD with the font family and size, margins, line width and brightness that is most like my ideal book. The screen is not taxing and page turns are less intrusive than a paper book.
Here is a valid comparison, "screen" versus "paper" goes nowhere. You cannot use a computer without reading its screen after all and no one can afford to give up computing. The world has moved on.