Yes! Every time you sit down to teach something, it inevitably changes the way you think about it. An important feature of Head First books (don't tell the competition...) is *motivation*. When we start work on a topic we begin with a survey of all of the material that's available, and then we start to ask *why* things work as they do. The best way to motivate a topic is to find a problem that a thing solves. Then you create a project to do something. Point out some difficulty that needs to be overcome. Then introduce the new thing that you *really* want to teach. And finally step through how to use the new thing.
This is closely related to an analytical technique called OODA: Observe, Orient, Decide, Act.
Consequently, when we started writing the first edition of HFAD we started to identify the *whys* behind the major topics, and the problems that each of the concepts solve. This has continued with each new addition.
For the changes in the new edition, Randy summed it up nicely: the switch from Java to Kotlin, and the use of new APIs. The new edition is a complete re-write of the book. There may be some similarities in the first chapter (things like how to create an app with Android Studio) but fairly quickly the book is very different from earlier versions. If you compare the tables of contents, you will see that they are quite different.
Thanks for the question.