How Mistral text gives itself away
Mistral AI is a French company. People know its models from the Le Chat assistant, but some of them are open and companies deploy them in their own internal tools. So text from Mistral may also come from someone who did not choose the model themselves.
The check judges only the text itself. It looks for even sentences, repeated paragraph structure and predictable word choice, so it does not matter which tool the text came from.