How to apply editor filter to posts with a specific custom post type

You can determine the current post type using get_post_type() inside the callback function hooked to wp_default_editor:

add_filter( 'wp_default_editor', 'wpse242896_wp_default_editor' );
function wpse242896_wp_default_editor( $editor ) {
    $post_type = get_post_type();

    if ( 'custom_post_type' === $post_type ) {
        return 'html';
    } else if ( 'other_post_type' === $post_type ) {
        return 'tinymce';
    }   

    return $editor;
}

Also, anonymous functions are generally discouraged because they can’t be unhooked very easily.