How did ChatGPT determine my location?

we need to make a distinction between

  1. The model
  2. The web app
  3. Third-party search app

When a search app is involved, results are likely relevant to the location
(because the search app receives your location likely from the Web app, not from the Model)

And then the’ location’ are ‘known’ by both you and the model.
The model assumes your location based on the third-party Search app results
then it generates the response and you see the response right away.

disclaimer: I am just making suggestions based on my humble developer experience