Indeed it is, they're not saying you have to make an account on that person's server, they're saying that you can make it on a different server, that's the point of federation you can join other servers that are connected to them. It's not to be fully open without any limitations, because if it were then content moderation would be impossible.

Services like Nostr have this problem, they are like the wild West where anything goes and you can't do anything about it. To some people that seems great but the fact of the matter is those services are filled with right-wing trolls and crypto scammers (likely plenty of other nasty stuff as well) because they cannot be moderated.