[Renate]

Most buttony Bluetooth thingies use HID over GATT (Bluetooth).
Since they are HID, like USB HID things, they have HID report descriptors.
That says what the buttons (or joysticks) do.
They can say that they are Usage 0x07 (Keyboard) or Usage 0x09 (Button)
When it's 0x07, your system knows what 'R' is and adopts the device as a system device.
When it's 0x09, your system only knows that it's some button and waits for some user proc to do something with it.

I've built both of these styles of Bluetooth devices for different purpose.
I have a utility for analyzing HID report descriptors, but I've never run it on Kobo.
If I can find my Kobo I'll see if I can get it running on that.

Edit: Duh! My Kobo Aura2 apparently has neither BT or USB OTG.