[jhowell]

The default for KF8 (azw3) is justified text. For KFX format the reader can select either justified or left aligned (ragged right).

You can force align left using css/styles, but that is discouraged by the Amazon Kindle Publishing Guidelines:

The body text in a reflowable Kindle book (fiction and non-fiction) must be all defaults. Amazon encourages content creators to use creative styles for headings, special paragraphs, footnotes, tables of contents, etc., but not for body text. For guidance on using embedded fonts, refer to section 9.3.8. The reason for this is that any styling on body text in the HTML will override the user’s preferred default reading settings. Users report such behavior as a poor reading experience.

I took a look at the free sample of the book you mentioned and the css stylesheet has the following:

p {
  margin:0;
  text-indent:0em;
  text-align:left;
  widows:2; 
  orphans:2;
}

So definitely forced left aligned.