That seems like a restrictive binary. Are there not other entities which generate text? What if a gorilla uses ASL that is transcribed? ELIZA could generate text, after a fashion, as a precursor to LLM. It seems like there's a number of automated processes that could take data and generate text, sort of, like weather reports, no?

So I think the only thing a mythical detector could determine would be LLM, or non-LLM, and let us take it from there. But detectors are bunk; I've had first-hand experience with that.