Widgets – how does the theme customizer GUI affect backend files

So uh, I feel like this has probably been answered before, but I couldn’t figure out how to actually phrase the question in a way that would give me the answer from a search engine.

WP 4.4 running twentysixteen (child)

Short version: how does making a change in the widget customizer GUI affect the backend php/template files? Which file is affected when I add a widget to one of the pre-defined widget areas?

Long version: Site works. I’m running it as a collection of seven static pages and one blog page. The eventual goal is to put the recent posts widget on one of the static pages (the home page) but none of the others.

To begin, I went into the widget customizer in the admin interface (Appearance –> Widgets) and put “Recent Posts” under “Content Bottom 1”. As expected, all of my static pages have this widget in the right place. Cool.

Now I’m trying to figure out what code changed as a result of this GUI action. Except I can’t find where it changed. None of the files appear to have been modified (FTP last modified), and I’ve compared before/after versions of a few suspects (inc/customizer.php, footer.php, page.php, sidebar-content-bottom.php, sidebar.php, template-parts/content-page.php) and they are all the same. So what is going on when I add the widget through the graphical interface? It has to be reflected somewhere in the code, right…. Am I just missing it?