I also think China recognizes that Trump negotiations are largely about dominance and Trump’s ability to convey a narrative that he “out-negotiated” the other guy, rather than an attempt to get the optimal deal for the US. When you’re negotiating with someone like that, maintaining “face” (ie preserving your position of respect within the negotiation) isn’t some mysterious Chinese concept: it’s just addressing Trump on his own terms, ie understanding that he only respects strength.
It isn't logic, it's emotion.
"disrespectful" is a term that the Chinese officials have used to describe US officials statements (1). I'm not reasoning my way to that term, I'm noting that the Chinese are there.
That and "Bowing to a bully is like drinking poison to quench thirst" (2)
I agree with sibling comment that saving face is it's "addressing Trump on his own terms" but I wouldn't say it's "just" that. It's also universal human psychology to react defiantly, expressed in regional idioms.
I agree that it's bizarre that it ended up there, nevertheless this is the USA's "art of the deal" working out as well as it's going to. With China calling the bluff.
1) https://www.youtube.com/watch?v=xNUs9G0sCFc
2) https://www.mediaite.com/news/china-responds-to-trump-tariff...