Yeah, I was somewhat surprised by those. "Classes" on domestic flights in the USSR?! And yeah, GUM was (and still is) a department store for Soviet citizens - https://en.wikipedia.org/wiki/GUM_(department_store).
No, long-distance trains had four classes: SV (two beds per cabin), Coupe (four beds per cabin), Platzkart (six beds per cabin) and Sitting (no beds, just benches). This classification goes back to Tzar (pre-revolution) times.
It has nothing to do with air transportation which has been developed in Soviet era, where everebody was equal.
