The Facebook clue is purported to disclose the "prize" for this hunt when solved. One should take this with a grain of salt---as there is no statement anywhere in the book that this is a treasure hunt, much less that there is a prize to be had. The author is under no obligation to give you anything. Is there a prize? Perhaps, but you shouldn't depend on it. I can't read the author's mind, so I don't know why this was done. But I have suspicions.

Below I detail a method to extract a message from the triangles. I'm not sure what the last statement of the clue is supposed to mean ("Anyway, good luck, and whatever you do, don't apply this to a certain page in the book!"). It's possible this methodology is used in the book, but I can't see a good place for it. I also can't see how it would have been helpful for Alchemist Dar either. The Hest was not aligned in a grid, and never really had 26 symbols to a row or column. So one would either have to impose a grid that was 26 wide or 26 high, or repeat the alphabet or something. Plus, given the sheer number of different symbols, you would have to pick out a particular symbol to have any hopes of getting a message. But I'm getting ahead of myself.

I will agree with the author's statement that the code is simple, once you know what is important. Both the colors of the sides and the triangles themselves are distracters. The only thing that matters is the locations of the vertices. The first thing to note is that the vertices are evenly spaced in the vertical direction. This implies a grid structure. One can construct a grid, with cells of size 20 pixels by 20 pixels, and overlay it on top of the triangles image, such that each vertex is in the center of a cell (within a +/- 2 pixel drawing error). Having done that, the vertices have a spread of 26 cells horizontally and 30 cells vertically, with each row of the grid containing one vertex. See the link below for an image.

Taking the columns to represent letters of the alphabet, the vertices then spell out a message from top to bottom: KNAJYMTZXFSIFSILTQIHTNSUQZXTSJ. This, of course, is not very helpful. But given how well the grid fits this drawing, it is assuredly the correct extraction method. So we look to see if this is some type of ciphertext. And after a bit of experimenting, one can see that a backwards shift of 5 gives the text: FIVETHOUSANDANDGOLDCOINPLUSONE. Why the extra step? Reasons, I guess. One could have come to this answer straight away by starting the alphabet used in the grid with a "V" instead of an "A", but I saw no cluing to that effect in the text that accompanied the image.

Anyway, it's not exactly clear how to interpret FIVE THOUSAND AND GOLD COIN PLUS ONE.