It's better for China to have the US overestimate China's nuclear arsenal than underestimate it.
Nuclear deterrence is a mind game in the end. You win nothing by hiding your arsenal or telling lies about having only a few nukes. It's not conventional war where you want to hide your troops to conduct surprise attacks. You DONT attack anyone with nukes, ever. China should rather boast that it has one million nukes and that nobody should get close to China or else they all go up somehow. China hiding their nuclear numbers really only shows that it is a sign of utmost weakness, and that China probably doesnt even have 100 nukes for the longest time (I wouldnt be surprised, seeing how xenophile the Deng and Hu era used to be), thereby exposing themselves to even more blackmail attempts.
It's like in the skid row; if you have a gun and muscles, you show them by open carry and wearing a muscle shirt to deter fentanyl zombies from attacking you. If you dont have them, you wear baggy hoodies and hope that nobody mugs you. China has for a long time done the mistake of doing latter instead of former. And see what happened with Taiwan.