It's just the default decentralized architecture. In a sense, relays are federated. The distinctions get lost on people not thinking deeply about it though.
Discussion
The wiki-page uses a rather broad and vague definition:
"A federation is a group of computing or network providers agreeing upon standards of operation in a collective fashion. "
Still, even then, i would object, the whole notion of federation is mostly Server Oriented Architecture related. Saying that because relays all share the understanding of same set of simple queries makes them federated is too much of a stretch. It might just be straight up incorrect if we start to wonder if relays are even ''a group of computing or network providers''. They don't do any compute, and they don't provide access to a network, they just provide access to data; the only logic going on in a relay is read/write access control.
It is kinda the whole point of Nostr, so I am easily agitated when i see indications of misunderstanding.
I have a similar gripe with the use of ''p2p'' in Bitcoin. People, on-chain bitcoin transactions are NOT peer to peer; miners are not your peers, they are intermediators. Now they are trust minimized and that so happens the be where the whole crux of this Bitcoin system resides; but if one says:
''Yeah well that is what i mean when i tell people Bitcoin has no intermediaries'', then i can't be sure if that is indeed what you mean, or that you missed the whole point all together and actually have all kinds of silly beliefs like that replace by fee is evil or that Nostr relies on federation.