That's not wrong, at least to the extent I understand ActivityPub. In practice, FidoNet was pretty hierarchical, with echo posts and mail flowing down/up through hubs to nodes in a tree. At least, it was strongly that way in the US, thanks to long-distance rates.

I've often compared nostr to UUUCP, which still had some hub-and-spoke tendencies, but which in my experience was a lot more mesh-like than Fido-technology networks. 

För context, I operated a BBS that was a hub for several Fido-type networks and a UUCP gateway from 1992 to 1998. Good times. 👍