(You can particularly tell from the "Conclusions" section. The formatting, where each list item starts with a few-word bolded summary, is already a strong hint, but the real issue is the repetitiveness of the list items. For bonus points there's a "not X, but Y", as well as a dash, albeit not an em dash.)
My native language is Polish. I conducted the original research and discovered the 'square root proof fabrication' during sessions in Polish. I then reproduced the effect in a clean session for this case study.
Since my written English is not fluent enough for a technical essay, I used Gemini as a translator and editor to structure my findings. I am aware of the irony of using an LLM to complain about LLM hallucinations, but it was the most efficient way to share these findings with an international audience.