I'm guessing they already had the plug (I myself have a small stockpile of extra Z-wave/wifi/Zigbee devices for when I inevitably need/want to hook something up

I'm guessing they already had the plug (I myself have a small stockpile of extra Z-wave/wifi/Zigbee devices for when I inevitably need/want to hook something up), so there wasn't a need to buy something else.