Isn’t this post specifically about fiction? When we say that a person “reads”, it normally means fiction.
I don’t see anything suggesting this is fiction only and I definitely don’t think “reads” means “reads fiction”.
What else do you read that can be measured in number of books? You wouldn’t do that for news articles, blog posts, or scientific papers. Cookbooks, textbooks and dictionaries are books, but you rarely read those from cover to cover, so you wouldn’t see people talking about the number of books they’ve read in that context.
Did you forget that non-fiction exists as a genre? Biographies and memoirs are very popular, for example.
I can’t tell if you’re trolling or if you just haven’t visited a library or bookstore in a while, but non-fiction books come to mind?
Sorry, I’m dumb. I do go to libraries quite often, but if I’m looking at the books, it’s to find something specific. I never browse the shelves.