Your Sitemap appears to be an HTML page. Please use a supported sitemap format i

Why do I get this error. If this plugin should make XMl specific sitemaps, why does Google Webmaster report “Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead.”

https://airportgyms.com/blog/sitemap.xml

I admit, when I hand make sitemaps, they look nothing like the above which is generated. So, why does this plugin generate a sitemap that is not proper XML that Google likes, yet it is called “Google XML sitemap”?

https://www.ads-software.com/plugins/google-sitemap-generator/