It working due to not being p2p has nothing to do with rebroadcasting, but that relays are literally web servers with SSL certificates and reachability. As such Nostr works in browsers where it's needed, also the "peers" being clients don't communicate with each other, they communicate as client-server infrastructure.
I believe "not P2P" refers not to clients not communicating with each other (which is fairly common) but relays not communicating with each other. And that creates problems because relays are out of sync. Rebroadcasting is one way to address the issue.
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