WordPress WP_Query/get_posts where post_title equals returns all results

I’ve created a custom post type called ‘snippets’ where there are snippets of data like ‘address’ that the client can change.

The title of the snippets are all unique:

I have created a simple function to return these snippets however it’s not working quite right and I’m not sure why.

Function:

function get_snippet($snippet_title) {
    $snippet_page = new WP_Query(array(
        'post_type' => 'snippets',
        'post_title' => $snippet_title
    ));
    return $snippet_page->posts[0]->post_content;
}

Here is an example call to the function:

echo get_snippet('footer_address');

The issue is:

It will always return all the snippets and not filter by post_title.

Even if I use get_posts() it will always return all snippets in the same order and will not return the single snippet based on the post_title.

The result is instead the equivalent to:

$snippet_page = new WP_Query(array(
    'post_type' => 'snippets'
));

Why will it not filter by ‘post_title’?

Thanks

(I am also using multisite)

Here is my custom post type init code:

function snippets() {
    $labels = array(
        'name'                => _x( 'Snippets', 'Post Type General Name', 'text_domain' ),
        'singular_name'       => _x( 'Snippet', 'Post Type Singular Name', 'text_domain' ),
        'menu_name'           => __( 'Snippets', 'text_domain' ),
        'name_admin_bar'      => __( 'Snippets', 'text_domain' ),
        'parent_item_colon'   => __( 'Parent Item:', 'text_domain' ),
        'all_items'           => __( 'All Snippets', 'text_domain' ),
        'add_new_item'        => __( 'Add New Snippet', 'text_domain' ),
        'add_new'             => __( 'Add New Snippet', 'text_domain' ),
        'new_item'            => __( 'New Snippet', 'text_domain' ),
        'edit_item'           => __( 'Edit Snippet', 'text_domain' ),
        'update_item'         => __( 'Update Snippet', 'text_domain' ),
        'view_item'           => __( 'View Snippet', 'text_domain' ),
        'search_items'        => __( 'Search Snippet', 'text_domain' ),
        'not_found'           => __( 'Not found', 'text_domain' ),
        'not_found_in_trash'  => __( 'Not found in Trash', 'text_domain' ),
    );
    $args = array(
        'label'               => __( 'snippets', 'text_domain' ),
        'description'         => __( 'For custom snippets of code/data.', 'text_domain' ),
        'labels'              => $labels,
        'supports'            => array( ),
        'hierarchical'        => false,
        'public'              => false,
        'show_ui'             => true,
        'show_in_menu'        => true,
        'menu_icon'           => 'dashicons-tagcloud',
        'menu_position'       => 5,
        'show_in_admin_bar'   => true,
        'show_in_nav_menus'   => false,
        'can_export'          => true,
        'has_archive'         => true,      
        'exclude_from_search' => true,
        'publicly_queryable'  => false,
        'capability_type'     => 'page',
    );
    register_post_type( 'snippets', $args );
}
add_action( 'init', 'snippets', 0 );