Technical laws are advised by people from technical backgrounds. And in the case of laws like this it is coming directly from technical experts at ASIO/ASIS.
Likewise it is irrelevant whether the Attorney General knows the technical definition of metadata since he isn't personally writing the law.
Much as they shouldn't ban a chemical additive to our foods without first understanding the nature and effects of that chemical (based on scientific research and evidence), then they shouldn't enact laws around privacy and data without understanding what that data itself contains. (He doesn't have to make the chemicals in a lab, he just needs to understand what it is/does).
The fact that the AG has no clear definition of what 'meta data' is, or cannot explain that to a reporter or the public really shakes my confidence that his limited understanding of 'meta data' includes elements that can personally identify someone (e.g. Does he think a phone number is 'meta data' or straight up 'personal data'? Because a phone number can be owned by more than one person, or is transferrable, does he think that is 'meta'?).
The AG should at least be able to give a broad definition of the scope of the laws that he is going to be responsible for upholding.
AG and Ministers set the strategic direction for the public sector. They operate at a sufficiently high level such that they will never be the experts and will never be across the subtleties of the policies. That's the job of the public servants.
Also the distinction between data and metadata is quite subtle and as someone who deals with this daily I make mistakes with it. So I don't expert the AG or really anyone to have the right answer every time.
Everyone generally agrees about how it is. The discussion is about how it should be.
We're talking about the kind of people who seriously say that the laws of mathematics don't hold weight in their jurisdiction. You can't defend that level of ignorance by just claiming it's not workable to have competent lawmakers.