It should come as no surprise that the lemmy.ml admin team took about 2 minutes to decide to pre-emptively block threats / Meta. Their transparent and opportunistic scheme to commodify the fediverse and it's users will not be allowed to proceed.
We strongly encourage other instance administrators to do the same, given the grave threat they pose to the fediverse.
Its like one is hotmail and the other is yahoo mail. They are free services/hosts that allow you to access the activityPub protocol. There are hundreds of such providers, and you can even host you own on your own services if you wanted to/were inclined.
Lemmy is a specific layout of the ActivityPub protocol. Continuing the metaphor, you could think of Lemmy like an email newsgroup. All the different lemmy instances display and sort the newsgroups the same way, which is to emulate reddit.