From communist viewpoint socialism is an intermediate stage before achieving communism. And in Soviet Union propaganda both terms were used interchangeably to d

From communist viewpoint socialism is an intermediate stage before achieving communism. And in Soviet Union propaganda both terms were used interchangeably to describe their side in the Cold War. And many self-described socialists in the West sympathised strongly with Soviets (even not being friendly with hardcore Stalinism), believing the USSR, and its satellites are the counterweight and alternative to the capitalist alliance united around the US. So there's no mistake, it's just a historical practice.