"US trade is a small fraction of the Chinese economy." is factually correct, if you want to compare trade surpluses, relative, absolute or some other factor and its impact to the Chinese economy, that's different from the proportion of Chinese economy that US trade represents. Let's not mix up totally different measures.
On a human scale If a portion of my income is removed, lets say all the companies whose stock I own decide to cancel their dividends so that's £2500 I won't be getting, and it will mean a bit of belt tightening like I won't replace my laptop this year, but as its not the main source of income, the house and car, food on the table won't be impacted. Would it be annoying? Yes, is it a big deal? Well in the grand scheme of things, No it's really not life changing!
While I agree broadly with your point, that is entirely the wrong analogy.
Income and wealth isn’t shared out equally in society as cells in a body share nutrition.
Loosing the US market won’t be the end of the world from a macroeconomic stand point for the whole Chinese economy, but it will mean millions of workers loosing their jobs and for most of them, that will be life changing since the impact will be system wide, so it is extremely unlikely they would be able to simply find another similar job with a different company as they normally would have been able to.
It is that social stability hit that has Beijing concerned more than the macroeconomics GDP hit.
The flip side is that Chinese trade to America is massively inflated - not in the normal semi-racist way western MSM say it is inflated, but rather inflated in that a huge percentage of those exports are not really Chinese to being with.
Much if not most of those Chinese exports are from foreign firms setting up production facilities in China to sell to America. The lion share of the revenue profits are not really retained in China.
Take the iPhone for example.
While each iPhone contribute $1k to the export statistics, the actual value Chinese workings make from that is likely only a few dollars directly, and probably no more than 100 even if you add in the whole supply chain impact.
As such, loosing $500bn in exports to the US would not mean the Chinese economy as a whole will be $500bn worse off, since a huge percentage of that 500bn would have been profits for foreign companies, and even more would have been pass through costs from importing energy, raw materials and sub components that goes into the finished products.