How does Drupal 7's SQL call for 'node' and retrieve an image?
It's utilizing a loaded entity to fill in these placeholder columns. Per the views_handler_field_field::query() docs:


  By default, the only columns added to the query are entity_id and
  entity_type. This is because other needed data is fetched by
  entity_load(). Other columns are added only if they are used in
  groupings, or if 'add fields to query' is specifically set to TRUE in
  the field definition.


In the post-execute phase, during views_handler_field_field::post_execute(),  you can see where the field values are dropped in from the entity values.