I can\'t get my head around, why offset seems to be forwarded from custom WP_Query in page template to the main query further down?!

From my functions.php

/**
 * ::: Filter \'Custom Post Type\' Archive Main Query :::
 */
add_action( \'pre_get_posts\', \'filter_cpt_posts\' );

function filter_cpt_posts( $query ) {
    if ( ! is_admin() && $query->is_main_query() && ! is_post_type_archive( \'cpt\' ) ) {
        return $query;
    } 
    else { // on is_post_type_archive( \'cpt\' )
        $query->set( \'offset\', \'1\' );
        return $query;
    }
}

From my archive-cpt.php:

<?php
    $loop_recent_post = new WP_Query( array(
        \'post_type\' => \'cpt\',
        \'posts_per_page\' => 1, // number of posts to display
        \'offset\' => 0
    ) );

    if ( $loop_recent_post->have_posts() ) {
        while ( $loop_recent_post->have_posts() ) { 
            $loop_recent_post->the_post(); 
?>

<!-- HTML Code -->

<?php wp_reset_postdata(); ?>

and further down:

<?php 
    //query_posts( \'post_type=cpt&offset=1\' ); //Get rid of `query_posts`
    if ( have_posts() ) { 
        while ( have_posts() ) {
            the_post();
?>

Posts start in main query with offset=0.

Why?

PS: Yes,

• I\'ve read When to use WP_query(), query_posts() and pre_get_posts -- that\'s the origin of why I came to alter query via pre_get_posts,
• and wp_reset_query() doesn\'t make a difference after WP_Query, I\'ve followed this rec.