I think they mean that a blockchain doesn't exist in a vacuum, someone has to write the code. While anyone can write a new client/protocol upgrade people won't

I think they mean that a blockchain doesn't exist in a vacuum, someone has to write the code. While anyone can write a new client/protocol upgrade people won't upgrade to just anyone's new client given how much value Bitcoin represents. No one has hard-control over bitcoin, but the leading dev group has some manner of soft/non-coercive control (by momentum alone).