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The device shows as made by the Hefei Bitland Information Co, which is a subsidiary of Shenzen. These guys make a bunch of internet connected devices. Could be anything from an IP camera, a Smart Hub, or a laptop. Since it's not connected right now, you can safely ignore it.
Since you have a Comcast gateway, you can log into your account at Xfinity xFi (if you have access) and manage your network from there. You can be notified if new devices connect to your network, for instance.
The gateway keeps a history of devices that connected to it. Unfortunately the only way to remove it from the list in your gateway's Admin Control Panel is to Reset the gateway to Factory settings. You'll likely lose any customized settings, although you will have the ability to restore most of it through Xfinity xFi.