In Chinese, there are two ways to refer to the word economy.
One is just 'economy' (jingji), the other 'citizen economy' (guomin jingji) if translated verbatim.
The Communists prefer to use the latter phrase, although it just means the same as 'economy'.
Now it becomes a headache for those translators. They are required to make a difference in translation between 'economy' and 'citizen economy', although there is no difference. Apparently they can't adopt 'citizen economy', for no one in the west would understand it.
My guess is, they decompose the word 'citizen' (guo min) furthur as guo means nation, min means people in Chinese, and hence the birth of 'national economy'. It has been in use since Mao era. The funny part is local Communist governments like to use the term too. When a county official talks about its 'citizen economy' or guomin jingji, he just means the local economy. However, you will most probably hear a translator put it as 'national economy' as my link above shows the documents are about Shanghai's local economy, but the term used is national economy.