You _might_ see some wifi information about that device, by Option-clicking on the wifi menu, then mouse across that item in the list of other wifi networks.
You should see about 12 lines of various wifi info on the network that YOU are connected to, and mousing across other networks will show similar information in a popup. That "device", whatever it is, might also show some wifi information when you pause your mouse on the device when you have the Option-click menu open.
You should see the same info, in your System Information, click on System Report, then down to Network/Wi-Fi. You will see a detailed list of your WiFi interface, and every network that your Wifi card "sees".
I don't have any devices that show up as a wifi device.
But, I might expect that a device that is not network-able appears as a device. If information appears, it may tell you the "PHY Mode" (such as 802.11n), and the channel that it is transmitting on.
The BSSID, if that is visible, might be used to determine the manufacturer of the device (or at least the manufacturer of the wireless chip.
Maybe something like a wireless webcam, or something else that uses a wireless connection