We're kind of getting in the weeds here, but basically what happens is that Windows reads the rambo.inf file and picks out the USB VID and PID (vendor ID and product Id) and then associates that with an actual driver. In this case "usbser.sys" which is used to talk to serial devices over USB. If the VID & PID are shared between the RAMPS & RAMBo and he's got the rambo "driver" installed, the RAMPS board will appear as he shows it in device manager. If memory serves, both the RAMPS & RAMBo boards use the same FTDI usb serial bridge chip, and that is the origin of the VID & PID values that the operating system is looking for.
Make sense?

g.