I'm sure that they meant to use the traditional definition of the word (i.e., new lore that explores the nature of the Twelve and how they will react to the 7th Umbral Era). It seems to me that the new white stones all over the world are a precursor to some sort of minor story thread that will come to the forefront in 1.23a and later, that will lead us into 2.0 proper.

The people who are calling the white stones "mythos" apparently just have no idea what the word means.