You are correct that the reference is a little obscure -- if my memory serves it's Plato's Phaedrus.
Plato argues, in a book, in the voice of his mentor Socrates, that books will destroy knowledge. And the reason is precisely to do with the thing that Socrates is famous for, his Socratic Method of asking his students (or rival politicians or anyone) questions about what they claimed to know, engaging them in a real discussion where we come to things that we agree about and then build that agreed knowledge-base incrementally. For Socrates, a book could never provide that experience; you cannot ask the book a question.
thanks to LLMs we can now ask books questions :)
That's actually kind of very similar to a passage in Zhuang Zi (ancient Chinese philosopher). He recounts this tale about a king and a wheel maker. The wheel maker asks what the king is doing, and the king proclaims he is reading. The wheel maker then goes on to inform the king how those books are just the trash of the ancients, and how he could not teach his son how to make a proper wheel, and the art "comes from the hand and is met by the heart". So anything that can be put down in books is certainly not true wisdom.
It also coincides with the Taoist philosophy (and actually somewhat Buddhist) of learning through actions and not speech. The most famous (if I recall the story correctly) of the Buddha teaching his disciples by smiling and twirling around a flower.
Kind of fascinating that these faraway places kind of arrived at the same ideas. Independently or not I think nobody would know but it does not matter.