No it isn't. It is literally the definition that is on wikipedia. That is a very good authority on definitions for things.
> At that point "censorship" is diluted to have no meaning beyond curation.
Sure it does. The meaning is quite clear in the article, which is a relevant authority on the issue.
Private companies can censor people. That is the definition, and the relevant authorities on the matter agree that it is.
Most definitions that you find with agree with me that private companies can censor people. This is not controversial, and most definitions agree with me.