Drupal - Difference between a bundle and a content type

Bundle is a generic term that applies to every entity Drupal or third-party modules define; content type is a specific term that applies to nodes.
Since nodes and content types were introduced a way before Drupal 7, content type was the first concept introduced, which then got expanded into the bundle concept when entities were introduced in Drupal 7.

So, yes, a content type is a bundle for the Node entity.