I've lived there and can say from experience China just makes stuff up. The local governments are responsible for reporting to higher ups and they don't want to miss targets, so they straight up lie. In reality it's a house of cards. You can lie about a 2% change once, and twice, and three times, but soon your lies compound and it's clear you didn't reduce emissions by the rate you reported. Only time will prove me correct about this. They do this with air quality regularly. Chinese official numbers of PM2.5 are regularly 30-50% lower than what the US embassy reports.