Makefiles

The current standard for generating a built distribution is the utilization of Drush and makefiles. Makefiles allow a user to define a specific version of Drupal core and other projects (such as themes, modules, and third-party libraries) that will make up a Drupal code base. It is not a dependency management workflow, like Composer, but is a build tool.

If you take a look at the Demo Framework's profile folder, you will see drupal-org.make and drupal-org-core.make. These are parsed by the Drupal.org packager to compile the code base and package it as a .zip or .tar.gz, like the one you downloaded.