HP, like many other manufacturers, ship machines with an operating system installed, plus a recovery partition to get you back to a factory build if things really get stuffed up badly.
There may also be a boot manager involved to allow you to switch to the recovery partition at boot time if the main boot drive is failing for some reason.
If you create an image of the main partition on such a system and then restore it to a machine with a clean hard disk and no boot manager, then that could account for the error.
However, you now have it working and I'm sure your testing regime will be a little more concise next time after your adventures with this machine!!