I also saw that and it seemed weird to me, I wanted to see how the author might have controlled for other media but it seems there were no controls or methodology beyond asking the question if they "read books" on an online survey which seems like a horrible way to gather any kind of reliable data - especially if the survey was in English. I can only assume though which is why I ask for a methodology that isn't paywalled since I'm not forking over 50 euros.

do you have a non-paywalled source, or at least a source where the actual graph, abstract or sources can be viewed without paying 50 euro? That data seems bizarre to me and I would be interested in how they reached it.