Basically, the idea is that when you take notes with a laptop, you can almost take down verbatim notes without really having to process the information, whereas taking notes with a pen and paper requires you to distill the information into more concise bits.
There's definitely something to this. In law school there were students with laptops who took down such detailed notes in class, the notes probably resembled a transcript of the lecture. Looking back, that's not the best way to learn.
I had a laptop in law school, and I would have probably done better if I had ditched it for a pen and pad.