Distributed networks are more of a mesh design, where every server runs all pieces of the application. Decentralized networks are only linked when they need to be and don't run every piece of the application.
Discussion
what are the pieces of the application that not need be run throughout, nostr-wise?
Hmm. Nostr isn't distributed because every client isn't the same nor does every relay hold a copy of all notes and events. In a distributed system, one can go down but everything continues to work because all of the data and services exist elsewhere.
is it okay to take clients into account, maybe better to focus on the protocol / relays? or should clients be taken into account too?
I would say that the Relayable relay network is distributed, because they have the same data in multiple locations around the world.
Clients can be distributed too. They'd need to use a cloud infrastructure or build their own.