No, I understand that people would know that Chinese existed far away. My point is that locally, PIE had neighbors, had variants, dialects, it had earlier forms, it was like a living language in a normal human context.

Maybe your brain works differently. I had this kind of misconception, imagining languages to be Pangea-like. That there used to be less linguistic diversity, there was a big uniform language (and perhaps a handful of others far away on the Earth) that later on fractured. But reality is more dynamic. PIE was just an ordinary language. And there was likely more linguistic diversity than today, due to less communication and travel opportunities and geographical features being more isolating.