Right now, the version data file (version.json) is only stored inside the SquashFS image. That is fine for most purposes, but means that image installation and upgrade tools have to mount both the ISO and the SqushFS image from inside it to read it.

If the file was also present inside the ISO itself, such scripts could tell right away if the image was for a wrong platform, for example. Since it's typically less than a kilobyte, it's not going to affect the image size.