I may be wrong, but I’m skeptical that this was a ‘Soviet’ base. Yugoslavia was never part of the Warsaw Pact and had a fairly tempestuous relationship with the Soviet Union. During the early 1950s during the last days of Stalin, Yugoslavia came close to shooting wars with their Warsaw Pact neighbors. The relationship between Yugoslavia and the Soviet Union may have thawed somewhat by the mid-1960s when this base was built, but I seriously doubt either trusted one another enough to permit a Soviet military base of this size to be built on Yugoslavian territory.
Yugoslavia was a communist dictatorship ruled by Marshal Tito from 1945 until his death in 1980. Tito was certainly less brutal than Stalin and probably slightly less brutal than later Soviet leaders, but that’s not a high bar. He undertook plenty of this sort of monumental building projects that every self-respecting megalomaniac communist dictator did. I’ve toured a nuclear-hardened bunker that Tito built outside of Sarajevo - sort of a less luxurious version of the Greenbrier.
The Yugoslav air force bought their top-line fighters from the Soviet Union, so there certainly could have been MiG’s housed at this base. They also had their own domestic aircraft industry and bought some aircraft from France during the cold war.
Again, I could be wrong but I have a strong guess that the base described in this article was a Yugoslav base, with aircraft that was sourced from the Soviet Union - and a young reporter who doesn’t know much about the Cold War just assumed it must be a Soviet base.
Yugoslavia certainly appeared the best of the communist countries with better and more everything for the ordinary citizen than their neighbors.
The fighters pictured definitely have the Yugoslavia national flag (1946-1992) on the vertical stabilizers.
“Stop sending people to kill me. We've already captured five of them, one of them with a bomb and another with a rifle… If you don't stop sending killers, I'll send one to Moscow, and I won't have to send another.” - Marshall Tito to Stalin