Yes, this is a theme issue. There is one list template, and it iterates over .Site.RegularPages which is a collection of every content page anywhere in your content directory.
the theme and documentation are far away from being complete. It is still work in progress and currently some features of Hugo aren’t supported.
This doesn’t inspire much confidence. Unless you’re comfortable creating and modifying templates, I would either (a) contact the theme author for assistance (https://github.com/geschke/hugo-tikva/issues), or (b) use a different theme.