I'm running the DIR 850L A1. Firmware 1.20 which appears to be the latest for my region (Canada). I'm using a cable modem.
It was a 192.168.0.xxx number that was showing up.
I've had a few times where an IP address appears in the Internet Sessions tab, but not on the wireless tab (all my devices are wireless), and not on the device info tab where I can see the name of the device. I'm curious as to why one would be appearing and how to identify it.