If we charitably assume "blockchain" has some engineering meaning (and it isn't purely a word for marketing/scamming) then there's some new aspect which sets it apart from the distributed-databases we've been able to make just fine for decades.
Uncontrolled participation is that key aspect. Without that linchpin, almost all the other new stuff becomes weirdly moot or actively detrimental.
> If you spin up a private bitcoin network, it's a blockchain even if nobody else knows or cares about it.
That's practically a contradiction in terms. It may describe the ancestry of the project, but it doesn't describe what/how it's being used.
Compare: "If you make a version of Napster/Gnutella with all the networking code disabled, it's still a Peer-to-Peer file sharing client even when only one person uses it."