Nope, no bug. You just only have access to the forums that correspond to your purchased products. That topic is from the Akita theme.
To edit the content of the 404 page you simply copy content-404.php to your Child theme and you can put whatever you want in there. The use of:
<?php echo themeblvd_get_local( '404' ); ?>
… simply allows for the default text in there to be accessible from the framework’s filter across all frontend text strings for use in plugins like this. — but you can remove it if you want after you’ve copied the file to your Child theme’s directory.