Display by tag from different post types

Question

may i suggest you use instead get_posts()?

example

$args_t10 = array(
  'tag_id' => 10,
);
$postslist_t10 = get_posts( $args_t10 ); ?>

$args_t10_v = array(
   'tag_id' => 10,
   'post_type' => 'videos'
);
$postslist_t10_v = get_posts( $args_t10_v );

you then can merge and filter the duplicates

$postmixed = array_merge($postslist_t10, $postslist_t10_v);
$uniqueposts = array_unique(postmixed);

reference

wp: get_posts() and parameters

php: array-unique() , array_merge