Same comments on all posts

I was able to reproduce the issue. It’s being caused by the loop in your code:

<?php if (have_posts()): ?>
  <?php while (have_posts()): ?>

Replace that standard loop with if ( have_comments() ) {..., like this:

<?php if ( have_comments() ) { ?>
    // The title, content and some other html here
    wp_list_comments(array( 'callback' => 'comments_callback'), get_comments());
<?php endif; ?>