Well, I think it's showing a decentralized network, not centralized. Maybe closer to federated, who knows, it's not clear. It's for sure not distributed though, while IPFS is a distributed file system.

If the graph contained at least one other link between the nodes than via the center one, it would make it more clear.

I think this famous graph (from Paul Baran https://www.rand.org/about/history/baran.html) does a good job of showing the difference: https://ipfs.io/ipfs/QmdYtMUTnz6vaQNRUAzhh8YiSSGzBCyQrCXE5Ag...

I think that the edges represent links across which information did/does flow, not where it can flow.

It's decentralized. Maybe you were referring to distributed networks?

https://cdn-images-1.medium.com/max/600/1*nnpzTe1hx74WKICL3G...

In a tree, any node can be chosen as the "root". That means any non-leaf node is a SPOF.

I think his point is that the existence of a SPOF obviates the need for distribution.

But it should be a DAG instead of a tree.