aggregator_views_data() contains two definitions for $data['aggregator_item']['iid']

I noticed that aggregator_views_data() contains two definitions for $data['aggregator_item']['iid']:

  $data['aggregator_item']['iid'] = array(
    'title' => t('Feed Item ID'),
    'help' => t('The unique ID of the aggregator item.'),
    'field' => array(
      'handler' => 'views_handler_field_numeric',
      'click sortable' => TRUE,
    ),
    'argument' => array(
      'handler' => 'views_handler_argument_numeric',
      'numeric' => TRUE,
    ),
    'filter' => array(
      'handler' => 'views_handler_filter_numeric',
    ),
    'sort' => array(
      'handler' => 'views_handler_sort',
    ),
  );

  // Item ID / 'iid'.
  $data['aggregator_item']['iid'] = array(
    'title' => t('Item ID'),
    'help' => t('The unique ID of the aggregator item.'),
    // The help that appears on the UI,
    // Information for displaying the iid.
    'field' => array(
      'handler' => 'views_handler_field_numeric',
      'click sortable' => TRUE,
    ),
    // Information for accepting a iid as an argument.
    'argument' => array(
      'handler' => 'views_handler_argument_aggregator_iid',
      'name field' => 'title',
      // The field to display in the summary.
      'numeric' => TRUE,
    ),
    // Information for accepting a nid as a filter.
    'filter' => array(
      'handler' => 'views_handler_filter_numeric',
    ),
    // Information for sorting on a nid.
    'sort' => array(
      'handler' => 'views_handler_sort',
    ),
  );