A random search has found a slightly more official source saying the passport needs only be valid for the length of stay.
https://bio.visaforchina.cn/MAN3_EN/...801073152.html
Q4: Are there requirements for the type and validity of entry documents?
A4: Foreigners must hold valid ordinary passports with a validity period meeting their travel needs in China. Travel documents other than ordinary passports, such as travel certificates or temporary/emergency documents, are not eligible for visa exemption.
Ita unfortunate that the details on the various Chinese Embassy websites are minimal for the visa free system, but probably understandable as it's outside of their sphere of influence and they ultimately want to sell visas. But the page linked above on visaforchina is probably as good as it gets.