Reading is one way people encounter ideas and learn, and so some people who read have a broad worldview and have absorbed the insights from books
People start to notice this, or perhaps those people attribute some other success to reading books. Enough association of this kind makes reading books high-status
Many people want to short-circuit this process to get status, so they optimize for reading a lot of books, or sometimes fake reading books
People who fake reading books for status are shown ridiculous when exposed
People who are allergic to and resent status nonsense conclude that bookshelves mean someone's a poser
This is obviously ridiculous. Many people have bookshelves because they simply need to store some books
The error committed here is, to me, a common one, overfocusing on the most salient case. I agree that it's icky when people do shit like fill shelves with books they've never and will never read as a status symbol. But are we really to assume that this is the most common reason to have a bookshelf? Or is it just the reason to which you have the strongest reaction, and thus stands out the most to you as a hypothesis?
With some additional information about a person, one might be able to conclude this given the bookshelf, but it hardly seems like enough evidence to come to this conclusion by itself