Prescriptivist views of language are alive, well and, apparently, worldwide. A student approached me yesterday. He's a bright kid in one of my strongest classes. He often comes to talk to me and, unlike some of the others, wants to talk about stuff that interests him... mainly movies and comics. This time though he started by telling me how sorry and ashamed he was. I was baffled. I had no idea what he was apologising for. After some questioning it seems that after our last conversation he had gone home and been working on a Chinese website that teaches English grammar. Here he had read that you must absolutely never say “I know” because it is appallingly rude. You must always say “I understand”. He had used the former rather than the latter when we were talking.
I reassured him that this is complete nonsense, just somebody's wrong-headed idea, but he didn't seem convinced.

Chinese culture, like the Japanese, is by all accounts rather more 'polite' than that of the West. I can see why it might be considered impolite to keep saying 'I know' when someone is speaking. It can be irritating. If they know already, why are you mentioning it to them?

It sounds like a minor culture-clash, where the Chinese believe that what might be to a westerner a minor irritation is more important than it really is.