Your text may well have been in the training corpus, but not searchable with whatever terms and search engine that LLM used after you prompted it. It doesn’t have recall of sources of documents comprising its training corpus, unless the source is widely cited in other of its training documents. Sourcing and provenance aren’t currently an intentional part of LLM training.

That may already have been obvious, and central to the complaint, but I was just knee-jerking to the anthropomorphic language.