This dialog shows the real world coordinates that were read from a World File. This is relevant only when the map file is a bitmap, and the bitmap file is georeferenced, i.e. a World File accompanies the bitmap file.
Real world coordinates for an OCAD map that is geo-referenced are read directly from the OCAD map file, and no World File accompanies an OCAD map file.
If you don't want to use real world coordinates for the bitmap, you can uncheck the checkbox.