s/fields/columns/ in getTableFields()

   * Gets the fields used to represent an entity in the IEF table.
   *
   * Modules can alter the output of this method through
   * hook_inline_entity_form_table_fields_alter().
   *
   * @param string[] $bundles
   *   An array of allowed bundles for this widget.
   *
   * @return array
   *   An array of fields keyed by field name. Each field is represented by an
   *   associative array containing the following keys:
   *   - type: 'label', 'field' or 'callback'.
   *   - label: the title of the table field's column in the IEF table.

The use of 'field' here is confusing, because it doesn't mean entity field, it means a column in the table, which isn't necessarily an entity field.

Best to replace with 'table column'.