Well, when it comes to Big Tech, it kinda is censorship, because they can deplatform you easily. But you can argue that Big Tech is mostly state-owned and therefore, not private entities.
Discussion
I think the question comes down to who controls the medium. If it’s government, then deplatforming is usually synonymous with censorship. If it’s a private entity, of whatever size, it’s their business choice to host content that serves their business’ bottom line.