All social groups are going to have some similarities. In any group the admission of a new member generates some excitement. The difference there is that here it seems to be genuine - I've never seen Simon or some other "leader" going around telling us we need to be more welcoming to new ones or telling us how to do that. In cults there are rules about how to live bomb people and you're judged by the group if you don't participate in the live bombing.
Furthermore, people can leave the forum without being punished by the group. I still talk to a few that have been booted from the forum for whatever reason, and I suffer no consequences for it. Others have left for years and maintained friendships with forum members or return and receive no judgement for having been absent.
Cults exist because they're fed by normal social behavior. It's how we're wired, so you should expect to see similarities everywhere. They'll just be at a much lower magnitude.