This is important to note, however you can somewhat infer it from the post: > I settled on adapting one of my more popular [blog posts][2] that I keep updated

This is important to note, however you can somewhat infer it from the post: > I settled on adapting one of my more popular [blog posts][2] that I keep updated through each version of iOS into a five book series (one for each topic of accessibility, design, UX, APIs and a catch all bonus one). They have a blog, around for years, and a post which is popular compared to others, constantly updated and comprehensive enough to be the basis of a book. Really doesn’t sound like an overnight thing. And not surprising to pass 10K followers when you have such a free offering.