Wonder if the TV would detect it as nonfunctional and still search for open networks that work.

If you can think if it, they can too.

As Samsung is essentially hostile beyond belief, and has thrown away all pretense of 'helping', I'd say yes.

I wouldn’t be surprised if they did but isn’t it illegal to connect to an open wifi if you haven’t got the explicit permission to do so?

All they need in that case is a signed contract with Comcast saying they’re allowed to connect to Xfinity networks.

Or buy a cheap good one ( eg Edgerouter Lite or X) and block them there, or put them on their own subnet.