Having no hint of which icon to display, the shell chooses the one with the lowest ID, or the first one that comes alphabetically. You have three icons in your executable: ICOFOLD, ICOOK and MAINICON. ICOFOLD is the one that is to be displayed in a shell folder.
The taskbar or the form icon are set by sending WM_SETICON
messages once your program runs. Hence there's no guesswork there.