Actually, it's not. State capitalism has absolutely no relation to how workers were used and abused by communist regimes.

For example, the following is from "The Failure of the Working Class" by Anton Pannekoek in 1946:

The workers of the world nowadays have two mighty foes, two hostile and suppressing powers over against them: the monopolistic capitalism of America and England, and Russian state capitalism. The former is drifting toward social dictatorship camouflaged in democratic forms; the latter proclaims dictatorship openly, formerly with the addition "of the proletariat," although nobody believes that any more.