how to prevent a theme from using templates of a sub themes (placed inside the parent theme dir)? my folder structure looks something like this:

 themes
└─  foo
   ├─  bar
   │  ├─  templates
   │  │  └─  node.html.twig
   │  └─  bar.info.yml
   ├─  templates
   │  └─  page.html.twig
   ├─  foo.info.yml
   └─  foo.libraries.yml


now I run a multisite. one site is using the foo theme and the other uses bar.

The site using the foo theme also invokes the template
/theme/foo/var/templates/node.html.twig


Why is that so?
I thought the foo theme only invokes templates inside its own templates folder? I expected this to be the point of the templates folder. Is that assumption wrong?
can I prevent this behavior without moving the subtheme somewhere else?
Themes are not allowed to be placed inside one another, as oppose to modules. Even though it works, there are undesired side effects.