I think they mean big-D "Distributed", i.e. in the sense that a DHT is Distributed. Decentralized in both a logical and political sense.

A big DynamoDB/Spanner deployment is great while you can guarantee some benevolent (or just not-malevolent) org around to host the deployment for everyone else. But technologies of this type do not have any answer for the key problem of "ensure the infra survives its own founding/maintaining org being co-opted + enshittified by parties hostile to the central purpose of the network."

Blockchains — and all the overhead and pain that comes with them — are basically what you get when you take the classical small-D distributed database design, and add the components necessary to get that extra property.