Ah, that makes sense! There are two kinds of random when it comes to setting up the slideshow. The random that you are using right now via metadata is part of the slideshow script and randomizes only the latest slides that are being loaded, 5 or however many you set in the quantity.
The other type of random you can use is in the WordPress post query, this will draw on all the slide posts, the 30ish you mention, and load 5 or however many you set at random.
You can use this second type of random by using a custom slideshow template. Just update the WP_Query function and add an "orderby" parameter:
$meteor_loop = new WP_Query( array(
'post_type' => 'slide',
'orderby' => 'rand',
'slideshow' => $slideshow,
'posts_per_page' => $meteor_options['slideshow_quantity']