Kefir build artifact is fully portable and agnostic to installation location. DESTDIR, prefix, etc are simply interpolated into launch script (template is here: https://git.sr.ht/~jprotopopov/kefir/tree/master/item/script...). So, no kefir binary itself does not know or care where it is installed, it gathers the information the environment variables provided by launch script.
The reason is that kefir supports portable builds which could be unpacked anywhere, so these path might even be relative.