This is nonsense. Self-censorship occurs whenever somebody censors himself. In polite conversation we might call it discretion (or valor). In a fiduciary or confidential relationship, we might call it adherence to the duty of confidentiality. In a contractual relationship, we would call it nondisclosure. In employment, on one hand we might call it professionalism—or self censorship on the other—depending on the context.

Regardless, the term "self-censorship" is not germane to or inherent in only citizen-government interactions.

People self-censor constantly on social media. You're not worried about the government taking a tweet out of context and driving your reputation into the ground, the mob of internet idiots has that covered. Fear of internet mobs causes people to censor themselves, and a definition of "censorship" that doesn't cover uses like that is not a particularly useful one.

Self-censorship as a term has value whenever people fear losing something that is important to them. With governments it might be their their career chances, personal freedom or even their life. With companies it might be your online identity, your data, your social contacts. Imagine being removed from Facebook/Google/Twitter/[your social network of choice] for writing the wrong post/email. While it is certainly orders of magnitude less threatening than being tortured by the secret police, it is still a deterrent.