"White bunny. Moon square." Do you understand what that means? Of course not! It's totally cryptic. Cryptic comments or messages are hard to understand because they seem to have a hidden meaning.
Cryptic is from Late Latin crypticus, from Greek kryptos, "hidden." This Greek adjective is the source of the English noun crypt, referring to a room under a church in which dead people are buried. That might account for why the word cryptic has an eerie tone to it.