Because the USSR was "authoritarian" and that makes them right wing.
Political Science is a real field of inquiry and Political Scientists are real scientists who deserve to be taken seriously, and other lies.
The shit political scientists say is just baffling. Like whether you like the USSR or not, defining right wing politics as being "authoritarian" is just bizzarely ignorant and weird. And, like, the definition of a nation state is partially an entity which effectively monopolizes the legitimate use of force within it's borders, so what the fuck does authoritarian even mean? Authority is the definition of a state, it's what makes a state a state. Fucks sake.
this is all articulated by arendt project of shoveling ussr nazi germany into authoritatian bucket and enlightened whitey empire into democracy bucket
With that goal in mind you can easily clock the person for those views (outside of anarchists, but they don't make whitey empire bucket separate)
At least... they claim not to