Weren’t there Soviet pilots and fighters in NK at the time?
I think an earlier poster was right, and the MIGs flew out of China across the Yalu river. I’m not sure they ever flew out of or landed in NK. I think the planes were supposed to be flown by Chinese and were supposedly sold to China by Russia. Whether either of these is true, or not, I have no idea.
My understanding from the 21st Century is that what Russia had done with Mad Mao in China, was being attempted by Mad Mao in Korea.
Sort-of like the rabid dog getting a pet of its own.