In Game of The Year edition, it says "Discover the Yeti Zombie" instead of "The Top Secret Zombie." Technically, this is so because it is a completely different achievement; it is also called Zombologist instead of Cryptozombologist, but in the Steam version, the description is the same as Zombologist.
If the player uses the I, Zombie hack and places a Zombie Yeti, the achievement will not be obtained.