I wouldn't put it past them to start trying to mesh network their way out of local network jail. Are your neighbors as diligent as you are about privacy and security?
I'm pretty sure at least a few of them do that already. I've seen too many reports of tech savvy people not knowing why they got updates when the TV has never been connected.
Very possible. Or maybe "just" connecting to any open wifi networks that might be available...
OTOH, I take "non-tech-savvy" reports with a healthy grain of salt. "Never been connected" could simply mean "I didn't plug it in to the Comcast box". Or "I connected Netflix, I didn't connect the TV".
Nothing a little bit of electronics surgery can't fix, clip the antenna or put a 50 ohm resistor in it's place. Better yet pull out the power amplifier or cut any power traces.