different post-class when template is loaded via ajax

You have to use this format:

FUNCTIONS.PHP

function theme_name_scripts() {

    wp_enqueue_script( 'script-name', get_bloginfo('stylesheet_directory') . '/js/min.js', array(), '1.0.0', true );
    wp_localize_script( 'script-name', 'ajax', array( 'url' => admin_url( 'admin-ajax.php' ) ) );
}

function ajax_callback() {
     get_event_list();
}

add_action( 'wp_enqueue_scripts', 'theme_name_scripts' );
add_action('wp_ajax_ajax', 'ajax_callback');
add_action('wp_ajax_nopriv_ajax', 'ajax_callback');

AJAX:

$.get(
    ajax.url, 
    {
        'action': 'ajax',
        'order' : 'DSC',
    }, 
    function( response, status ) {
        $('ul.event-items').append(response);
        }
);

You may use this line to explicitly include the wr_event class:

 <article id="event-<?php the_ID(); ?>" <?php echo event_canceled($post) ? post_class('wrapper canceled wr_event') : post_class('wrapper wr_event'); ?>>

and also add die(); at the end of the template file to avoid the zero displayed.