Mid 1991 is a fascinating little historical freeze-frame moment to get such a perspective from, it's pretty interesting.

Let's take a look at the state of the Cold War and geopolitics as of that time. First off, while the USSR did still officially exist on paper at the time it was clear to anyone paying attention that it had a limited lifetime and at best would continue onward as something very different than what it had been. Through the late 1980s there was a softening of relations between the West and the Communist Bloc. Various reforms such as Perestroika had opened up the Soviet Union and softened hard line communist rule and isolation. Western bands were even able to tour the Soviet Union and played concerts in Moscow. Peace talks and strategic arms limitation talks were also happening and proving fruitful, from the Reykjavik Summit in 1986 to the Intermediate-Range Nuclear Forces Treaty of 1987 and then the first START treaty (which was signed just immediately after T2 was released but followed the well understood trend of softening relations away from war and toward peace at the time).

This coincided with a dramatic escalation in more open relationships with the West following the collapse of the Eastern Bloc, even more so than had existed with Perestroika. Western goods flowed into the Soviet Union. A McDonalds was opened in Moscow in January of 1990, a few months later a Pizza Hut opened there as well. In late 1989 Pepsi ended up in an agreement where they took ownership of 20 Soviet naval warships to be scrapped as payment for syrup deliveries. At this point the future trajectory of this relationship seemed clear.

Then there is the wave of revolutions and independence movements. In the late '80s these movements were still contentious, but after the fall of the Berlin Wall in late 1989 everything started going one way: away from hard line communist rule and more toward democracy and independence. East Germany basically ended concomitant with the opening of the border with the West and this was followed extremely rapidly by the adoption of plans to reunify Germany after free elections in East Germany in mid 1990 and then agreement to reunify in August of that year. Meanwhile, you have the complete crumbling of the Communist Bloc in Eastern Europe in Poland, Hungary, Czechoslovakia, Bulgaria, and Romania. By the end of 1989 the Eastern Bloc as it had existed, the foothold that the Soviet Union had to project Communist geopolitical influence, had ended. In early 1991 the Warsaw Pact was declared effectively null and void and later that year it was officially ended.

Within the USSR the first free elections in the republics (Edit: see /u/Awesomeuser90's correction below) were held in 1990, with the communist party losing control over many republics. Many of these republics declared their independence and began a messy process that resulted in military occupation of these breakaway republics from 1990 through the dissolution of the USSR in late 1991. Even though the ultimate fate of the breakaway Soviet republics had yet to be decided in mid 1991 at that point the assumption was that things would trend mostly as they had with the Eastern Bloc. And though the Soviet leadership in Moscow had sent in tanks and military forces to maintain control over the republics it was still very clear that it was playing by a different set of rules than it had during the Prague Spring of '68.

Meanwhile, you have the other major geopolitical events of late 1990 and early 1991: the Iraqi invasion of Kuwait and the Gulf War. I won't go into all the details of the Gulf War but there are a few key points. One is that even though Iraq had been an ally of the Soviet Union throughout the Cold War, and much of their military equipment (especially tanks) were Soviet, they received zero support from the USSR during the conflict. Another is that the Soviet Union went along with UN Security Council resolutions which demanded Iraq leave Kuwait and also codified Iraq's defeat and obligations to disarm after the end of the conflict. These events are pretty remarkable because prior to the 1990s such a conflict would have been seen as a prime opportunity by the Soviets to weaken America by aiding Iraq. The outcome of the Gulf War reified the pronouncements of George HW Bush and Gorbachev on the transition of geopolitics to a "New World Order" with the ending of the Cold War. Additionally, the utter dominance of US forces, equipment, and tactics against what had been seen as, at least on paper, some fractional approximation of Soviet conventional military power began the process of elevating America to the status of unilateral "hyperpower" (at least until 9/11 changed the game).

So, even though late 1990 to early 1991 when Terminator 2 was filmed preceded the height of the early-90s period of "good feelings" between the US and Russia, after the USSR had been officially dissolved and with Boris Yeltsin as America's favorite drunk Russian uncle, it was still a common sentiment in America that the Soviet Union was on its way out and was no longer the bogeyman it had once been.

Interestingly, the timing of Terminator 2 put it in a very precarious place in terms of the perception of political relations between the US and "The Russians". It was filmed/written early enough that it was buoyed by the wave of independence and democracy sweeping the Eastern Bloc as well as the end of the Cold War and the opening of Russia to cultural and economic interchange with the West (e.g. McDonald's in Moscow). But it was filmed just early enough to miss out on many of the messy details of Russian occupation of the Baltic SSRs (or of the last push of hardline communists in Russia) which wasn't resolved until late 1991.

I will say that while plenty of people look at 1991 as "prior to the end of the Cold War", this was not exactly how people would have understood the geopolitical situation in early to mid 1991.

Very technically, the Cold War, in the sense of the geopolitical confrontation between the United States and Union of Soviet Socialist Republics that had been a mainstay of the globe since the end of World War II, was formally ended at the Malta Summit of December 2-3, 1989. This was more or less the message of both President Bush and President Gorbachev at the news conference following the summit.

The idea that the Cold War ended with the fall of the Soviet Union (and usually the "fall of the Soviet Union" itself gets dated to when Gorbachev resigned on December 25, 1991, although you could make an argument for earlier or later dates) is something of a retcon, albeit one that was adopted extremely quickly. President Bush himself in his State of the Union address on January 28, 1992 stated "By the Grace of God, America won the Cold War" - referring to the previous month's collapse. This was as much political posturing in a presidential election year as anything else - Bush was not pursuing the dissolution of the USSR as a political objective, and even on August 1, 1991 had spoken before the Ukrainian Supreme Soviet urging for Soviet unity and against nationalist secession, in the so-called "Chicken Kiev" speech.

Anyway, back to Arnold and Terminator 2. When it was released on July 3, 1991, there was every reason to think that the Cold War was over, and that the Soviet Union would continue as a "normal" country with productive relations with the United States. Maybe not as an ally, but certainly in a reasonably non-confrontational and businesslike relationship of the sort that the United States and China have had (at least until recently). In 1991 the USSR no longer had satellites in Eastern Europe, was drawing down its military, was in a fair bit of economic and political turmoil, but had held reasonably free elections in 1989 (with similar elections at the republic level the following year), and was working towards establishing a new constitutional order under the Novo-Ogarevo talks (it was the official signing of the new constitution that the coup plotters stopped with their coup attempt on August 19, 1991). Some kind of change was appearing inevitable, but there was no reason to think that the Cold War was on, and plenty of those who heavily followed the increasingly complicated situation in the USSR at the beginning of 1991 thought that it would continue in some post-Cold War form.