The article talks about surveillance by the companies, and how they track you visiting web pages. All known stuff.
But the big hint here is surveillance within ebooks. And there is no hint about how this might be done.
I have edited literally thousands of ebooks from many sources. I've found traces of java script in one or two, and in neither case were the scripts anything that could track you. And most ebook formats and readers don't support scripts anyway.
Reading online, sure, they have you in focus. But reading an ebook offline? I've seen no evidence of it. Neither have many thousands of users on the relevant Reddit or Mobilread platforms.
Not that they would not like to do this! But I don't think they are there yet.
If anybody has seen a mechanism, like an example of code in the ebook, I'd love to see it.