My understanding is that it was the latter. From the ABC (Australia):

How was the data accessed?

As the government understands it, in this case, OpenAI gave an agent a "benign" task of trying to do research about public medicines spending.

The model then searched the internet widely for the information, and came across the Services Australia portal.

It then asked questions of the portal, but the portal didn't provide it with the requested information. As a result, it gained unauthorised access and secured information that wasn't public.