That is most likely Lemmy Federate at work. Since Lemmy does not automatically federate the communities to other instances, someone from your instance needs to subscribe to that community for your instance to start receiving new content for that community. Lemmy Federate basically does that for registered instances. The community’s instance probably has the auto add feature enabled in Lemmy Federate, which is why it got 50 members in a few minutes of the community’s creation.
That is most likely Lemmy Federate at work. Since Lemmy does not automatically federate the communities to other instances, someone from your instance needs to subscribe to that community for your instance to start receiving new content for that community. Lemmy Federate basically does that for registered instances. The community’s instance probably has the auto add feature enabled in Lemmy Federate, which is why it got 50 members in a few minutes of the community’s creation.