Nature is a well-regarded peer-reviewed journal. They don’t just publish any slop that gets submitted to them, they have quality standards. Plus the reasons people usually give for why this would be the case don’t explain why it wouldn’t also happen to non-Chinese institutions. It might just be racism, but there are ways a reasonable person could come to have an unreasonable belief. It could be the case that where-ever this person is finding Chinese articles is highlighting only lower quality Chinese articles, and only higher quality non-Chinese articles. Like if they’re getting articles from some kind of news outlet or something, and not just looking through articles about a specific topic they need.

Edit: I guess it could also be a translation thing. Translations from Chinese works can often be complete ass (my experience is with books but I imagine it would also apply to research article), so that might affect his opinion even if the methodology is sound.