I saw that too and wondered why they were called “Russian” fighters instead of “Soviet” fighters. I don’t think that was a mistake.
Even if they were Russian pilots, it is hard to see why that should be classified today.
I know back then, there were concerns about the USSR entering the conflict, and if so, that is likely why.
But how would we have known they were Soviet? Did we have intelligence? Could we hear their chatter? Did they have markings of the Soviet Air Force? If so, what were they doing conducting operations over the Korean peninsula?
If they were Soviet, we should keep in mind how concerned we were with getting into a nuclear conflict with them at the time.
“...wondered why they were called “Russian” fighters instead of “Soviet” fighters. I don’t think that was a mistake.”
We’ve always used “Russian” and “Soviet” pretty much interchangeably.