not entirely.
the difference is, your identity by which everyone knows you does not include the name of any relay AND your data is stored in a particular server and you better hope the instance operator knows how to properly do backups.
in nostr your identity is your `nsec` keypair which works with any client and any relay. you dont have to choose one.
And you cant get your data from any of them and have additional backup servers... this gets even more true with peer to peer.