The IP was requested by the router and the router is providing addresses to the other computers. So the router might get an IP address of 66.x.x.x (which is the IP on the cable network) and then give out addresses in the 192.x.x.x (or whatever you configured the router to distribute). Then the router routes the traffic from the appropriate 192 to the appropriate 66 to the cable system who routes it to the internet backbone (eventually).