It's fake news:
Foreign Ministry Spokesperson's Remarks
Q: Is it true that the Chinese Embassy in the DPRK two weeks ago advised Chinese citizens living in the DPRK to leave the country?
A: It is fake news according to what we have learnt. The Chinese Embassy in the DPRK has never issued any such kind of notice. China and the DPRK are close neighbors with normal people-to-people exchanges. There are Chinese citizens entering and exiting the DPRK every day, and that is quite normal.