Related to https://gist.github.com/jchristopher/8558947 — once you have told SearchWP to consider arbitrary meta, you will need to give the meta keys you used a weight in the SearchWP settings. To ensure those keys show up in the Custom Field dropdown on the SearchWP settings page, we can use the searchwp_custom_field_keys filter

gistfile1.php

<?php
 
function my_searchwp_author_meta_keys( $keys )
{
    // the keys we used to store author meta (see https://gist.github.com/jchristopher/8558947 for more info)
    $my_custom_author_meta_keys = array( 
        'my_author_meta_nicename', 
        'my_author_meta_display_name', 
        'my_author_meta_nickname', 
        'my_author_meta_first_name', 
        'my_author_meta_last_name', 
        'my_author_meta_bio' 
    );
    
    // merge my custom meta keys with the existing keys
    $keys = array_merge( $keys, $my_custom_author_meta_keys );
    
    // make sure there aren't any duplicates
    $keys = array_unique( $keys );
    
    return $keys;
}
 
add_filter( 'searchwp_custom_field_keys', 'my_searchwp_author_meta_keys', 10, 1 );