Strictly speaking, you're correct -- but it also highlights that not all censorship is wrong or bad. It can very easily be a valid exercise of free speech rights.

Twitter (or any social media) moderating people's posts isn't wrong, for instance. Nobody's rights are being infringed when they do this. You might disagree with their moderation policies, but that's a different thing altogether.

Legally speaking in the US, it's only censorship when the government is doing it.