Does the plugin delete the media attachments too?

yes but only if they are attached to the post (so not when added in the media library)

	/**
	 * Actually deletes post and its attachments
	 */
	private function delete_post_and_attachments($post_id, $force_delete) {
		$atts = get_children(
		[
		 'post_parent' => $post_id,
		 'post_status' => 'inherit',
		 'post_type' => 'attachment'
		 ]
         	);
		 if ($atts) {
		 	foreach ($atts as $att) {
		 		// Deletes this attachment
		 		wp_delete_attachment($att->ID, $force_delete);
		 	}
		 }

		 // Now delete post
		 wp_delete_post($post_id, $force_delete);
	}