subscriptions to communities on other instances

So.. I noticed in the "all" feed that it's really not feeds from ALL of the lemmy communities out there.. Then I read on the self hosted feed that the size of the instance grows depending on what users are subscribed to. Does that mean that the things I see on all are only what others signed in to this instance are subscribing to? The instance here is caching feeds from other communities? And thereby what I subscribe to will be seen in the "all" feed for others signed in here?