meta_key & meta_value not working with get_pages and custom taxonomy

Custom taxonomies are not meta values, but rather their own thing. I don’t think wp_list_pages() or get_pages() can query based on a taxonomy, so I’d recommend using WP_Query instead:

<?php
$relevant_pages_args = array(
    'post_type' => 'page',
    'posts_per_page' => -1,
    'post_parent' => 65,
    'tax_query' => array(
        array(
            'taxonomy' => 'relevance',
            'field' => 'slug',
            'terms' => 'alumni'
        )
    )
);

$relevant_pages = new WP_Query( $relevant_pages_args );

if( $relevant_pages->have_posts() ) : while( $relevant_pages->have_posts() ) : $relevant_pages->the_post(); ?>

    <a href="https://wordpress.stackexchange.com/questions/52967/<?php the_permalink(); ?>"><?php the_title(); ?></a>

<?php endwhile; endif; wp_reset_postdata(); ?>