The fix is detailed in the original post - by doubling the vertical dimension of the image’s canvas from 340px to 680px, and leaving the bottom half empty (or pasting the second sheet in the post into the bottom half, if you’d like), RPG Maker is able to properly separate the sprites for a character to use. The sprites in that sheet are only one row of character sprites - properly twelve images wide, but only four tall. RPG Maker handles the separation of those into individual segments on its own. Basically, a grid that’s eight characters tall by twelve characters wide. The original post pretty much says it all - basically, RPG Maker expects there to be two four-image-tall rows of character animations, each with four three-image-wide columns that define the animation.
