Yup, pretty much. I’ll lazypaste the response an instance admin made after I asked a similar question recently:
Probably the community follower bot which several instances subscribe to. It’s a way of automating new communities discovery
Comment on How do some communities get like 50 members minutes after its creation?
AwesomeLowlander@sh.itjust.works 3 days ago
Communities will only show up on remote servers if an account from that server is subscribed to that community. To increase accessibility and enhance the user experience, many servers have a bot account that will automatically subscribe to new communities so that they can start receiving posts in that community. That accounts for the majority of the instant subscribers on new communities.
neidu3@sh.itjust.works 2 days ago
rikudou@lemmings.world 2 days ago
Yep, this is the reason, the service that facilitates this is called Lemmy Federate.