Ouch! Apple altered recovery a few times. The first version setup a hidden partition on the drive which in your case was lost. To add to this when you install Windows the boot blocks on the drive are altered so macOS won’t install or boot correctly. You need to fully wipe the disk and start again. The last issue with BootCamp is a bit wonky! It sits within a special folder with The Windows Mac drivers and part of Windows. The rest sits in a second partition.
Keek in mind you are limited to OS-X Lion (10.7.5) and Apple's Boot Camp 4 formally supports the 32-bit versions of Windows XP SP2, Windows Vista, and Windows 7. You can’t run the newer BootCamp or newer Windows on this older MacMini.