I think they mean being the first user to subscribe to a community on their instance. If no one else has subscribed yet it won't federate over. First subscriber needs to search the whole community url then after any others can find it in search just by name.
Instances only federate communities once a user has subscribed to them. Otherwise instances would be inundated with hundreds of communities no one even wants.
It is communities. You can be federated with another instance but until a user subscribes to a specific community it won't federate or appear in all
What is fetching
I think they mean being the first user to subscribe to a community on their instance. If no one else has subscribed yet it won't federate over. First subscriber needs to search the whole community url then after any others can find it in search just by name.
Instances only federate communities once a user has subscribed to them. Otherwise instances would be inundated with hundreds of communities no one even wants.