Blocked is not quite the right word here. Nobody has blocked them. Nothing is stopping you from going over there to see the content they have. You can visit that instance directly and sign up on that instance if you like.

What is better to say is that they may not be federated with the Lemmy instance you connect to. This just means that your instance does not aggregate things from there and will not show the posts from that server in your feeds.

Right now the site is 404'ing, but this is not because of federation or blocking. Their site is just down for some reason.