So I commented on a post on lemmy.world, and somebody from lemmy.ml replied to my comment.

I was finally able to reply to their comment in turn by using the reply symbol under their post in my notifications. I couldn't reply before because clicking on their comment took me over to lemmy.ml and I thought I would be able to sign in with my credentials from here and post, but I think I understand now that that isn't possible. Every instance has its own registered users and you can't cross-post, you can only reply on the federated thread on your own instance and wait for it to be federated over to the user from the other side.

When I look at their post now, my comment shows up on lemmy.ml. So the thread was federated over to lemmy.ml from here, I guess?

I have not registered on lemmy.ml, just on lemmy.world.

Did I comment on lemmy.world and it got federated over to .ml?

Because I can't comment on the post on lemmy.ml, but that's expected I guess, since I'm only registered here.

Does this make sense?

Sorry if I'm just blabbering on here, but I'm still a bit confused about how all of this works exactly. Typing this out helps me understand this.

Is anybody facing similar issues of not quite understanding what they're doing?

I will attach a screenshot.