I just ran wi-fi inspector and it listed 2 devices that i have no idea what they are. It listed the wifi connected devices that should be there and one device named lenovo and one device named unknown device. As far as I know, I have no lenovo device at my house.
You should be able to get more detailed information on the suspicious devices in the scan list by clicking on the entry. That should at least show you the assigned IP and MAC addresses for a given item. If you are familiar with the configuration of your network, that could help you identify the network hardware that wi-fi inspector is seeing. I remember in a previous version of the product, a network card I’d installed was identified by the chip maker so its possible that something of that nature is producing the unexpected results.