That's because Windows Phone 8.1 Update 2 supports Bluetooth keyboards. Here's how it all works. You first need to first connect the keyboard as you would any other Bluetooth device like a headset.

It only takes a few quick steps to connect your Windows PC to a mouse, keyboard, or other accessory via Bluetooth.

On a Mac, you can just hit the Bluetooth icon in the menu bar and hit "Set Up a Device". Your computer will scan for devices, and your keyboard or mouse should pop up.

You can connect a wireless keyboard to a Mac or PC using Bluetooth, as long as the keyboard is charged and in pairing mode.

If your Bluetooth device won't connect in Windows and you receive Can’t pair Bluetooth keyboard, Check the PIN and try connecting again message; see this post.