That’s a cultural difference though. It’s like when people believe that you’re going to be declared a witch and burned at the stake if you time travelled to the past and talked about iPhones. Just like in any culture today, they’d just assume you’re nuts, laugh and move on.
However, people generally underestimate how culture differs. The idea of belonging to a certain group was vital in the Middle Ages. And that’s something modern people would probably not put much thought in if time travel was possible.
Single digit thousands of years is a drop in the bucket for evolution. The people back then were largely the same as they are now. They just lived in different cultures. Modern innovations are all motivated by a need. Some form of pressure to come up with a solution. Pre civilization societies just don’t have a need. It’s accounting and management of a large population that requires some form of book keeping and written records. There is no reason to believe, without need and cultural precedence, that writing would have been invented by societies in earlier stages.
In the same way classical physics isn’t wrong about the world compared to modern physics, calling this the first writing system is just in the context of our current understanding of the world of the past. We can be pedantic about the details but going by our current understanding, this is what makes sense. This understanding might change but it’s is needlessly pedantic, especially in a field like this that is less „cold hard truth“-ish compared to physics.