I'd gently point out we're 4 questions into "what about if you went about it stupidly and actually learned nothing?"
It's entirely possible they learned nothing and they're missing huge parts.
But we're sort of at the point where in order to ignore their self-reported experience, we're asking philosophical questions that amount to "how can you know you know if you don't know what you don't know and definitely don't know everything?"
More existentialism than interlocution.
If we decide our interlocutor can't be relied upon, what is discussion?
Would we have the same question if they said they did it from a book?
If they did do it from a book, how would we know if the book they read was missing something that we thought was crucial?
I didn't think that was what was being discussed.
I was attempting to imply that with high-quality literature, it is often reviewed by humans who have some sort of knowledge about a particular topic or are willing to cross reference it with existing literature. The reader often does this as well.
For low-effort literature, this is often not the case, and can lead to things like https://en.wikipedia.org/wiki/Gell-Mann_amnesia_effect where a trained observer can point out that something is wrong, but an untrained observer cannot perceive what is incorrect.
IMO, this is adjacent to what human agents interacting with language models experience often. It isn't wrong about everything, but the nuance is enough to introduce some poor underlying thought patterns while learning.