I think the message was claiming something else, specifically that each classification was given a score of how confident the model was in the answer and the answers were given 99.9%+ in those cases.
Seems to have major biases against who knows what sentence structures. Even without trying to make it say fake, some of my messages and text I write in it are pretty confident I'm GPT-2...
With 5 samples, we have no way to assess whether the app’s 99.9% self-assessment is remotely well calibrated. (As noted above, 5/5 is also consistent with a model that is right 50% of the time.)
See the app: https://huggingface.co/openai-detector/ - it gives a response as % chance it's genetic or chat bot.