get_posts from a category id doesn’t work

It’s

'post_date'

not

'date'

so

$args = array( 'numberposts' => $items, 'post_type'=>'portfolio','orderby' => 'post_date','order'=>'DESC','category' => 5 );
$posts = get_posts($args);
foreach($posts as $post){
    setup_postdata($post);
    $return_html="......";
}

Should fix you up.