China's government policy and central bank tightly control the exchange rate and only allow it to fluctuate within certain predetermined bands.

"An official re-adjustment of the mid-point rate for the trading band is announced by the country's Foreign Exchange Trading Center at 9:15 a.m. each day, Shanghai time."

https://www.fxcm.com/uk/insights/how-does-china-control-exch...

So each day the government says what the currency should be and gives traders very little wiggle room.

As for the first question should they or shouldn't they do it, I don't know.