It seems the pilots were Russian.
From the article—”The national security peril soon dawned on Navy command who discovered Williams had engaged the Soviet Air Force.
Migs flying in the Chinese and Korean air forces were known to be flown by Soviet volunteers but this was an escalation with potential to turn the Cold War hot.”
Not just Russian. That happened often in Korea,Russian flying Chinese MIGS from Manchuria, but these guys flew from Vladivostok not Manchuria. The MIGS were Soviet AF not Chinese or NK. That’s what made keeping it quiet important. Some Soviet colonel had let his emotion get the best of him and attacked USN warplanes over North Korea.