So the conspiracy theorist insane people behind the "Bill gates put 5g in your veins" discourse has recently appropriated the term "pureblood" as some sort of insane cope to think they have the high ground.
This is from Harry Potter and tl;dr is a movement for wizards similar to white replacement theory that's popular with racists now.
So 4chan is trying to push the symbol for the "deathly hallows" and the ancap color scheme in order to get media attention to the term because it is also from Harry Potter
And it's "funny" because they associated the symbol with right-wing extremists, and the media will report that right-wing extremists are using it.
Am I up to speed here?