Our detectives are back with the following intel on this WordPress site
Unfortunately we could not identify the theme this site is using.
We could identify 2 plugins (there might be more) - Better WordPress Google XML Sitemaps (support Sitemap Index, Multi-site and Google News) and wp-rocket
A WordPress XML Sitemap plugin that comes with support for Sitemap Index, Multi-site and Google News sitemap. Image sitemap is supported, too.