Monstrous Misnomer

While looking over the 5th Edition Monster Manual, I was drawn to the entries of several iconic monsters to see how they appeared in this iteration of the game.  In the past, I was occasionally frustrated when I would search the online 3.5 Edition System Reference Document (SRD) for a monster's stats only to find it didn't have an entry on the site.  It turns out that there are some creatures so iconic of the D&D brand that they are considered the intellectual property of Wizards of the Coast and among these are the beholder, the carrion crawler, the mind flayer, and the yuan-ti.

One of the things that struck me as most odd about the yuan-ti's entry was the classification of the three types of snake people your party may encounter.  My observation led me to look into the publication history of these serpentine folk.  These monsters have their origins in the 1981 AD&D module Dwellers of the Forbidden City and were later detailed in the Monster Manual 2 and the November '89 issue of Dragon magazine.

Now (as far as I can tell) there is no explanation of the strange choice in terminology that has been used to describe the three different castes of yuan-ti society: the abominations, the malisons (formerly politically incorrectly known as the half-breeds), and the purebloods.  My concern is that I just named those three castes in descending order of station within their snake society- meaning that this race of snake folk are ruled by those that they call "abominations" while the ones that are called "purebloods" are the bottom rung of the societal ladder.

This game is always teaching me new words.

To confuse the issue even more, the 5th edition Monster Manual describes the abominations as the ones that "most closely resemble the race as the serpent gods intended it" and the purebloods are yuan -ti that "closely resemble humans."  If you closely resemble the god(s) that your society most reveres, then who would call you an abomination?  If you were so unlike all of the other members of your race and in fact almost looked completely like another race entirely, then why would you be called a pureblood?  The only explanation I can come up with is that this reptilian civilization takes the bizarro approach where everything said is the opposite of what is meant...  That ssseems like a great idea.

See what I did there?

Is there something that I'm missing?  Some logic in this design choice that I'm failing to grasp?  Please, let me know on Twitter @critthulhu or by emailing critthulhu@gmail.com.