If there's configuration for base product, it's layered. Let's not force people to say it again.
I ran into this recently because the documented Minimal Config Example does not have release_is_layered, yet Pungi does require this setting.
release_is_layered
Commit ce066707 fixes this issue
Metadata Update from @lsedlar: - Issue set to the milestone: 4.1.38
This issue has been migrated to Fedora Forge: https://forge.fedoraproject.org/pungi/pungi/issues/977
Please continue any further discussion there.