is my account and all its posts, comments, activity and bookmarks just gonna be gone?
No. Your account and it's posts, comment, and activity will live on because they're copied to other instances. You won't be able to log on though. That's why the post suggests making a new account and updating your bio before the shut down. Exporting and importing your settings will probably carry over bookmarks.
No, if you think of censorship as a sliding scale with total freedom to say anything on one side and extremely rigid and locked down on the other, it doesn't take much moving away from the anything goes side to want to block racists.