What does this mean?

switch ($op) {
    case 'form':
      $form = array(
        '#theme' => 'link_field_settings',
      );

...

Could you please tell me what does '#theme' => 'link_field_settings', mean? Thanks. I am in the process to develop a similar module.

Does that mean that the setting form is going to call theme_link_field_settings to render its UI and takes $form as its parameter?

Thanks!