Blog and sitemap creating extra pages via tag

Hi and excuse me if this has been asked but a search yielded no usable results witch might be because I lack the specific terms to search for.

I use the Gantry 5 Helium template and have a blog_list added to the main menu, and the blog contains several pages.
When creating a sitemap (from an external service) I notice it comes up with pages like:
/tag:wordpress
/tag:joomla
/tag:getgrav
/tag:cms
etc

I do not use these tags and do not need them. But I cannot figure out where these tags are generated and how to get rid of them/change them into something more usefull. Can anyone help me?

sorry if this is a silly question.. I am a Grav fan and have been using it for a year or two but this issue is driving me mad..

Thank you for taking the time to share your insights..

The words "wordpress" and "joomla" are probably defined somewhere in Gantry or inside a theme. In cases like these I use a search application to search inside files on my local filesystem. On MacOS I use EasyFind but I'm sure there are many alike tools and for Windows as well.