The Russians' usage of the term antifascist certainly didn't age well, but it's worth noting that "fascists" is how all people in the world referred to certain Germans and Italians for a period of 25 years all up until 1945 (and the affected folks didn't mind that - in fact, the term was invented in Italy in 1915 and then adopted by Mussolini in 1918 and by Hitler in 1923 [0]). So for Russians to refer to Germans who didn't join them as fascists is just a continuation of how the term had been used for a long time.
By 1961, it was definitely unfair to continue using the term in its original meaning, and at this point it was certainly the Russian government pushing their agenda a lot more strongly than the general population would have on its own. But it's not like everyone was strictly opposed to it either - the horrors of the war had created in Eastern Europe such deep resentment towards Germany that it would take a lot more than 16 years to get over that. In fact, my grandpa lived until the 90s and still called every German a fascist.
Far-left and far-right ideologies have more in common than many people realize (including the people within those factions). They are both based on the principle on low tolerance, and as such they are well-aligned on the idea of strict enforcement of their ideologies.
There are some hilarious misconceptions that members of those factions have about their own ideologies. Far-left is against the police brutality, but there is a 100 year history of perfect correlation between leftist regimes and policy brutality.
Far-right is against government interventions in all economic matters, but that also has never materialized anywhere else.
The bottom line is that anything that's far-something requires suppression of the society's natural tendency to return to the center.
The Wilson and Attlee governments in the UK would be very surprised to hear there's a "100 year history of perfect correlation".
They were certainly leftist. Many would consider them far leftist today. (Of course they weren't, but that doesn't mean the label wouldn't be applied.)
Neither was legendary for police brutality. That came later, with Thatcher's response to the Miner's Strike and the poll tax riots - among others.
I have a hard time considering a government that ruled over and fought bitterly to protect a global capitalist empire as truly 'leftist,' unlike the UK's geopolitical enemies of the time.
It is also likely that subjects of certain British colonies would have a substantially different opinion on police violence.
Where is the line at to be drawn between nationalism and fascist ultra nationalism? The rise in nationalism in many countries is one thing, but as that nationalism becomes stronger it is too easy to see it as drifting into fascist territory.
By 1961, it was definitely unfair to continue using the term in its original meaning, and at this point it was certainly the Russian government pushing their agenda a lot more strongly than the general population would have on its own. But it's not like everyone was strictly opposed to it either - the horrors of the war had created in Eastern Europe such deep resentment towards Germany that it would take a lot more than 16 years to get over that. In fact, my grandpa lived until the 90s and still called every German a fascist.
[0] https://en.wikipedia.org/wiki/Fascism