It's both; it's aimed at hosting a single user program on another userspace, but also seems to have its own kernel as well?

The "North" part seems to be what I think you'd traditionally think of as a library OS, and then the "South" part seems to be shims to use various userlands and TEEs as the host (rather than the bare hardware in your example).

I'm really confused by the complete lack of documentation and examples, though. I think the "runners" are the closest thing there is.

The reddit conversation seems to allude to you being correct.