Your Blocked User list is stored within the instance you’re on (for you it’s lemmy.ml), and not shared to anyone else. Note that the people you block can see your posts through various ways due to the nature of ActivityPub.

The people banned from communities and instances are visible to all instances. You can see the modlog on lemmy.world as a reference, where moderation from lemmy.ml communities are visible on its modlog.

The story behind this tracker is really funny. An advertisement meant as a Santa hotline accidentally misprinted their number and linked to a confidential number in NORAD. Lots of kids started calling it, and people in command were unavoidably confused. After figuring out what happened, they decided to host an actual santa hotline in said number, which later evolved into this tracker.