"Do not look in the file of incriminating evidence to see whether or not the accused rose up against the Soviets with arms or words. Ask him instead to which class he belongs, what is his background, his education, his profession. These are the questions that will determine the fate of the accused. That is the meaning and essence of the Red Terror."
You're right, it's not literally saying they're subhuman, but it seems pretty close. Actions are irrelevant, only identity matters. That doesn't have anything to do with perceived threats. Only a crazy person would think that someone of a certain class was a threat regardless of their actions unless they believed that there were implicit differences that basically amounted to those of different class not deserving life. And yeah I think it's definitely a genocide.
It's very similar to the genocide in Cambodia where they killed people who wore glasses (in addition to all the others) because they assumed that if they wore glasses it must be because they were literate, and all intellectuals were the enemies of the working class. We read an account of a man who had been a leftist but was sent to a camp because of his glasses. Once again, they didn't literally say people were subhuman, but they sought to attribute fundamental differences to something as superficial as eyesight.
In my first comment, I was mostly talking about people coming to believe that a group of people was fundamentally different in a way that common decency no longer applies, that you no longer give them even the consideration you would give criminals, you just send them off to die because they are irredeemable for something as stupid as what family they were born into or whether or not they wore glasses.
So, no, it wasn't about any kind of a fundamental difference. That ideology didn't believe that there was any group of people to which common decency no longer applies. They believed that common decency no longer applies to anyone, because revolutionary necessity requires it. People who were deemed dangerous to that necessity were killed not because they were deemed subhuman, but solely because they were deemed to be a danger. They even reflected it in the criminal code - it didn't speak of "punishment", but rather of "means of social protection", and death penalty was euphemistically referred to as "the highest measure of social protection".
The Stalinist regime was plenty violent and systematically kills millions of people, but calling it genocide doesn't make sense because that wasn't what it was by definition unless you want to compare it to Nazi germany which killed millions more.
But anyway, originally we were talking about "the worst atrocities in the history of the world", not genocide specifically. So it's reasonable to assume that genocide in this context is used in a colloquial meaning - i.e. any kind of intentional mass murder by some group metric, not necessarily ethnicity.