The idea behind this method of importing content is flexibility and the ability to update/re-import dfiferent entities. It's another way to get data from anywhere is by using this combination of Drupal 8 (and eventually Drupal 9)'s Queue API along with drush commands.

The Content Import Module

You'll want to start with a regular, old Drupal 8 module. Add a src directory and add yourself a directory for drush commands and another for your queue workers. Check out this article if you need a better idea of how queue workers are created: