welcome to the forum!
Sorry I had to remove the date you said! If correct or not, the publisher did not allow me as the author to publish the date and doesn't want anybody else to to it. This prevents us from discussions with them, and most important, I don't want to stop them to offer the LaTeX book for free just because information leaked. They could easily replace and make a promotion with any other of their thousands books instead.
It's only a matter of few days, since their current promotion activity ends March 5.
To answer your question: actually I started writing it in LaTeX, but I had to follow the publisher's requirements. They got a workflow which they used for more than a thousand of books, and they don't make a difference because the book content is about LaTeX. Would be similar to expect that a book about Libre Office is typeset using that, a book about Scribus is written with Scribus, ... all editors stick to the workflow. And this is
- authors deliver Word (!) format using a big set of publisher formatting macros
- editors and reviewers use word tracking changes and commenting for reviewing
- it get's imported exclusively using the publishers macros in Adobe Indesign
- Indesign is the final tool for typesetting.
I already got a hate comment on amazon roughly like "what can a LaTeX book be like if it wasn't printed using LaTeX". That comment "author" did not speak about content. Well, it's not respecting that a LaTeX author wrote it, only referring to the publisher's process. I'm glad that this Indesign/Word-only publisher has this book in the collection. I don't get much money for the book, it's about enough to pay for the two servers I run for some forums, blogs, TeX galleries. I assume, nobody looks there for a LaTeX book, but: the publisher routinely does promotion bundles, so people take it by chance. For example, one buys a PHP book, gets the offer "take a second book for half price", looks around seeing a lot of strange topics find's the LaTeX book and takes that.
Back to the strange publisher's routine: they don't take PDF! They allow authors to deliver images only in JPG oder PNG format. Crazy. I had an extensive discussion with them. I delivered all images in high quality scalable PDF format. They were not able to adapt it, they used bitmap images. They said, it would look good in print. They are not aware of high expectations of LaTeX users! So in the ebook, you will notice some images will look like screenshots. Please don't complain to me, but only directly to the publisher ... I was sad myself that they put bitmaps in the book, getting not optimal image quality, and I could not get out of the contract. I made my peace with it knowing people liked the book contents, and the book paid the servers where also this forum runs.
Good news: this year, I will publish another LaTeX book. Same publisher - well, they asked me, no other publisher did yet. They will get again some bitmaps, but in high resolution (whatever they make of it), the content will be interesting new stuff.