> Training data is not just about learning facts, but also (mainly?) about how language works, how people talk, etc.

All of that and more, all at the same time.

Attribution at inference level is bound to work more-less the same way as humans attribute things during conversations: "As ${attribution} said, ${some quote}", or "I remember reading about it in ${attribution-1} - ${some statements}; ... or maybe it was in ${attribution-2}?...". Such attributions are often wrong, as people hallucinate^Wmisremember where they saw or heard something.

RAG obviously can work for this, as well as other solutions involving retrieving, finding or confirming sources. That's just like when a human actually looks up the source when citing something - and has similar caveats and costs.