They’re not saying something else nor denying reality.

To be clear what they are saying is “Bitcoin, not crypto”, making them into distinct classes; ie different things.

That both words refer to cryptocurrencies is not the relevant point of the statement. “Gold, not metals” would convey the same - it implies a distinction and delineation in what the speaker is referring to, a superior/inferior.

I know some languages would equate “not” to simply a negative of the following word, but that’s not how it’s being used in this context in English.