Easiest reason is the 'introduction particle', blub which we don't have in English, for subordinate clauses.

I think 'taught ChatGPT to invent a' is hyperbolic though, this is more like 'taught ChatGPT my invented' - the only thing it invents itself are the 'relex' word->word mappings.

I agree the author/experimenter seems to have done most of the conlanging here. The development benefit comes, I think, from having the AI reflect back the work so the experimenter can correct output and consider their conlanging decisions (eg use vowels for case marking).

I'm now wondering how the AI would cope with one of my conlangs. I have example sentences already - https://docs.google.com/document/d/1YT9KzgvFu8DNWVL02t1NGgRS...

Isn't `blub` more or less equivalent to `that` or `which`?