How to list tags from custom post type attachments?

get_the_tags() function in deed returns only terms of ‘post_tag’ taxonomy (tags). If you’d like to get terms of another taxonomies, you’d have to use get_the_terms function (http://codex.wordpress.org/Function_Reference/get_the_terms)

$custom_post_tags = get_the_terms( get_the_ID(), 'type' ); //type is a name of custom taxonomy

or you can use wp_get_object_terms function (http://codex.wordpress.org/Function_Reference/wp_get_object_terms) where you can define more than one taxonomy

$custom_post_tags = wp_get_object_terms( get_the_ID(), array( 'type', 'post_tag', 'category' ) );

Hope I got your question corretly….