Humans did research and remembered sources before the Internet was a thing.

But also, can you give an example where an LLM with access to the Internet can find a primary source?

I don't think learning to refer to sources is something inherently impossible for LLMs, but it is very different to the kind of implicit knowledge they seem to excel at.

They just paste in the first link then or some other programmed heuristic, they aren't like a human that puts in effort to find something relevant. An LLM with internet access isn't smarter than just asking google search.