We also know that groups without writing systems were historically able to adopt writing systems rather quickly, which is, I think, rather good evidence that writing is a technology, not a point of speciation.
Going back to Ancient Greece, Socrates didn't even believe in the effectiveness of writing for communication of knowledge. My poetry professor used to spend some time on this, because it's intimately tied to the art of poetry. He would cite a number of studies showing our emotional responses are intimately tied to our language processing, and that humans are wired to emotionally respond to, and remember, stories.
Even before writing, oral histories were passed down for many generations. For an extreme example, see: https://www.sapiens.org/language/oral-tradition/ .
I won't pretend to know what makes us human, but ultimately I believe it has to be rooted in something neurological, not technological.
As I mentioned in another comment, I'm skeptical of the questions that imply a kind of species essentialism, suggesting that there's such a thing as a one particular trait that distinctly makes us human. I think the real answer to questions like that are vast convergences of immense clusters of facts relating to our evolutionary history and our morphology and so on. I don't think there's any like one single thing. But I do think in comparison to other species a rather elegant way of distinguishing this is to put to our written traditions which as far as I know don't really have any precedent. And if that doesn't blow you away in terms of how miraculous and special are evolutionary trajectory is, I don't suspect anything would. But the important thing is that you don't need a species essentialism to be impressed with who and what we are.