That doesn't make any sense... you're using your own modem and router but see an extra wifi signal? I have the same setup on Comcast and don't remember seeing such a thing. I don't even understand how that would be possible.
I'm not sure, and I'm not positive that it's happening, but it's the only "XFinity free WiFi" SSID in my area. Everyone else is on Verizon (I almost switched, but Comcast offers me more and better free stuff for the same cost in the end, despite shitty bandwidth throttling).
I know that when I moved to this place (account transfer from CA to MD), I brought my same equipment, same service, but rather than the shitbox "digital box" that I was using, I now have the X1 box (also shitty--this is the first replacement within 6 months and it started breaking again), I now have to have the X1 box active (it is always on) to get any internet signal. It has that separate powered coax box that must be plugged into the power outlet as well as the primary cable output in the house. If you have one, you know what I'm talking about.
It's the first time I've had this sort of setup, and it rather pisses me off. No internet without TV....fuck that. Always on cable box that breaks once per day, forcing reset. The nice thing about the box is that it outputs HD that I don't have to pay for (the previous shitbox had HDMI out, but it was inactive in my non-HD service. This one works with my non-HD service). Also, "basic cable" here isn't simply Network/already free OTA channels (like with Comcast in CA or TWC in NC), but also includes AMC, History, Discovery,CNN/Fox/Food Network and some random channels like that.