> it’s fundamentally impossible to do with the current state of technology
Maybe.
> Imagine the word “democracy”, would you be able to tell me where you’ve first learned the definition of it
Sure, it was elementary school history lessons when we were learning about the greeks.
> be able to provide a direct citation of it
Naturally. I would just look it up in one of the many dictionaries. Copy the definition and tell you which dictionary it was copied from.
> What about the thousands of other instances where you’ve seen that word defined?
What about them? When you are providing sources you are not required to provide all the sources you ever read, nor is it desireable.
> The only viable way would be to do a reverse lookup of the output to find out if there’s a similar worded content on the internet
They don’t have to do that. It is enough if they do a plagiarism search within their own training dataset.