When you say gateway , are you referring to the modem / router combination device ?
The two were possibly one wired mac and a wireless mac, which would have accounted for the double entry.
At the same time , the only logical reason on a simplified intranet for conflict , could be a static Ip was set on the wired side, and not listed outside of the dhcp range , before the laptop was connected to the router / modem or of course any time in between, but you would have to know this, unless someone else had control of the laptop before you. Again , if you had a PPOE connection before comcast, which required a static IP per device or almost any other reason want or need, for a static IP.
This would account for you not seeing the IP within the router, as the static IP after restore, is again , within the dhcp range, or on a subnet -- ie: 192.168.2.1/24 Vs. 192.168.1.1/24 /32 ect
Check your IP is set to dhcp and within the comcast dhcp range.
Running XP ?