I was prompted to create a "backup" disk as well, but I chose not to create one.
I suspect that this is to create a backup of your system from the recovery partition. It would allow you later to reinstall the OS at the level as it came out of the box. This disk (usually 2 DVDs) is bootable and that's what the geek squad people seem to refer to.
The 6GB Image Backup is something else. It is an image of your system and if you want to use it, you need the recovery CD which you can create from the Windows 7 imaging facility. The fact that it is smaller than your system is a matter of compression.
But as Richard already said, if you want to go into imaging, Paragon is a better option although I prefer Free Macrium
. Here is my video tutorial
for it if you want to use it.