Show "Related Articles" for Pages, not just Posts

Please help, I use Illdy theme which uses nice function/class for listing “Related Articles” under Posts. It is the file \themes\illdy\inc\components\related-posts\class.mt-related-posts.php

However I would like to make it work for Pages as well. What do I need to change to make it work for Pages?

The call is done with:
do_action( 'mtl_single_after_content' );

I tried changing
wp_get_post_categories( $post->ID )
to
wp_get_post_categories( $page->ID )

but then the loading times get very long.

Here is the entire code of the function/class:

/**
 * Class MTL_Related_Posts_Output
 *
 * This file does the social sharing handling for the Muscle Core Lite Framework
 *
 * @author		Cristian Raiber
 * @copyright	(c) Copyright by Macho Themes
 * @link		http://www.machothemes.com
 * @package 	Muscle Core Lite
 * @since		Version 1.0.0
 */

// @todo : more effects for hover images
// @todo: pull in more than post title & date

if( !function_exists( 'MTL_CallRelatedPostsClass' ) ) {
    /**
     *
     * Gets called only if the "display related posts" option is checked
     * in the back-end
     *
     * @since   1.0.0
     *
     */
    function MTL_CallRelatedPostsClass()
    {
        $display_related_blog_posts = get_theme_mod('illdy_enable_related_blog_posts', 1);

        if ($display_related_blog_posts == 1) {

            // instantiate the class & load everything else
            MTL_Related_Posts_Output::getInstance();
        }
    }
    add_action( 'wp_loaded', 'MTL_CallRelatedPostsClass');
}

if( !class_exists( 'MTL_Related_Posts_Output' ) ) {

	/**
	 * Class MTL_Related_Posts_Output
	 */
	class MTL_Related_Posts_Output {

		/**
		 * @var Singleton The reference to *Singleton* instance of this class
		 */
		private static $instance;

		/**
		 *
		 */
		protected function __construct() {
			add_action( 'mtl_single_after_content', array( $this, 'output_related_posts' ), 3 );
		}

		/**
		 * Returns the *Singleton* instance of this class.
		 *
		 * @return Singleton The *Singleton* instance.
		 */
		public static function getInstance() {
			if ( null === static::$instance ) {
				static::$instance = new static();
			}

			return static::$instance;
		}

		/**
		 * Private clone method to prevent cloning of the instance of the
		 * *Singleton* instance.
		 *
		 * @return void
		 */
		private function __clone() {
		}

		/**
		 * Private unserialize method to prevent unserializing of the *Singleton*
		 * instance.
		 *
		 * @return void
		 */
		private function __wakeup() {
		}

		/**
		 * Render related posts carousel
		 *
		 * @return string                    HTML markup to display related posts
		 **/
		function output_related_posts() {
			global $post;

			$output = '';

			$post_query_args = array (
				'post_type'					=> array( 'post' ),
				'category__in'				=> wp_get_post_categories( $post->ID ),
				'nopaging'					=> false,
				'posts_per_page'			=> 3,
				'ignore_sticky_posts'		=> true,
				'cache_results'				=> true,
				'update_post_meta_cache'	=> true,
				'update_post_term_cache'	=> true,
				'post__not_in'				=> array( $post->ID ),
				'meta_key'					=> '_thumbnail_id'
			);

			$post_query = new WP_Query( $post_query_args );

			if( $post_query->have_posts() ) {
				$output .= '<div class="blog-post-related-articles">';
					$output .= '<div class="row">';
						$output .= '<div class="col-sm-12">';
							$output .= '<div class="related-article-title">';
								$output .= __( 'Related Articles', 'illdy' );
							$output .= '</div><!--/.related-article-title-->';
						$output .= '</div><!--/.col-sm-12-->';

						while( $post_query->have_posts() ) {
							$post_query->the_post();

							$post_thumbnail = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'illdy-blog-post-related-articles' );

							$output .= '<div class="col-sm-4">';
								$output .= '<a href="'. esc_url( get_permalink() ) .'" title="'. esc_attr( get_the_title() ) .'" class="related-post" style="background-image: url('. ( $post_thumbnail ? esc_url( $post_thumbnail[0] ) : '' ) .');">';
									$output .= '<span class="related-post-title">'. esc_html( get_the_title() ) .'</span>';
								$output .= '</a><!--/.related-post-->';
							$output .= '</div><!--/.col-sm-4-->';
						}
					$output .= '</div><!--/.row-->';
				$output .= '</div><!--/.blog-post-related-articles-->';
			}

			wp_reset_postdata();

			echo $output;
		}
	}
}

Thank you kindly for any helpful advice.

Closing this inquiry, by kind help from Reddit user on r/Wordpress. For anyone else in the same problem, all that has to be changed in above code is the following:

the line:
post_type' => array( 'post' )

Change it to:
post_type' => array( 'post', 'page' )

Best,