It is all generic layers, the base USB stuff is called a "Human Interface Device", controllers/keyboards/mice/etc. all show up as a HID to the OS. But you need some way to standardise the input and map the device side events to the host side, so the OS will have a mapping layer above the base USB layer that turns a generic HID into a "controller device" that an app can use.

As you can see from the patch, that's all they're doing. They're adding the USB IDs of these controllers to the mapping layer so instead of being shown as a "Generic HID", they're shown as "Generic Xbox Controller". Doing so also means the controller layer can drive the devices specifically, e.g. xbox controllers need a special handshake to enable the xbox button, the base generic input layer doesn't need to know that stuff.