The PR that added it says it uses GPT3. I’m not really up to date on the differences between ChatGPT and GPT3 but my understanding is that they are different.
This one I can definitively answer - the integration has zero knowledge about the HA instance its connected to. As the docs you linked earlier say:
This conversation agent is unable to control your house. It can only query information that has been provided by Home Assistant. To be able to answer questions about your house, Home Assistant will need to provide OpenAI with the details of your house, which include areas, devices and their states.
So it cannot answer any questions about the specific HA instance the integration is installed in (i.e. your house). It has not been provided that information.