Socialism predates communism. Communism is influenced by it, but it's not an "intermediary state", it's not even a "state". It's a simple principle that the people who labor should control (the usual term is "own" but that's a little misleading) the means of production. There's a second component that is usually unsaid that ends up being a principle of the ideology in practice - that cooperation is encouraged instead of competition.
Unions are one example (and go right to the heart of why I said "own" is misleading), because unions seek to increase the power of workers within a business that would otherwise be controlled by its shareholders.
Another is the government owning businesses on the grounds the government and the people are one. But that only works (ideologically) if the country is genuinely democratic, and it still doesn't work well because there's quite a dilution of ownership going on there, leading to a substantial gap between the people doing the job and their control over it.
The purest form of socialism in most democratic countries is the cooperative movement, where businesses are owned by the people who work for them. (Not to be confused with cooperatives where the customers own the company, for some reason.) That is literally the workers owning the means of production.
Basically the author of this piece has probably gotten their terminology from a combination of Ayn Rand and online people who think "socialismism is where the government does it, the more the government does the more socialistismist it is. Like Nazi Germany. Did you know Nazi has the word socialist in it? Clearly a socialist movement! And Unions are bad because they are socialist, therefore must be Hitler and Stalin who are totally the same guy, I mean, they are both famously mustachioed And dictators And had "socialistismistism" in the name of their movements" and repeat this crap all the time.
Anyway, Unions are not some intermediate step towards Marxism. Not even close. Unions, cooperative movements, and, yes, the government owning some businesses, have historically been ways to prevent countries from falling to Marxism by addressing workers concerns, using some socialism to stave off a far more problematic and less likely to leave anyone happy thing. And there's nothing wrong with that. Perhaps if rich people stopped forgetting who made them rich, they'd spend less time worrying at night about regime change.