Discussion of this on reddit leads me to believe that at least some Samsung TVs would connect to any available open wifi networks.

I purposefully didn't give my Sony tv (android) my wifi password. A few weeks later it prompted me to install a firmware update, and I saw it was connected to my home wifi. How? Best I can guess is another android device shared credentials with the TV.

I blocked that stupid thing at the router. I don't need firmware updates for my TV.

Is there anyone else in your house who might have put in the credentials? That seems like a big security hole if Android will just share wifi credentials with other random Android devices.

Why would you have open networks? Anyone can monitor their traffic.

I can't exactly control my neighbors.

Right. The only thing I've ever done using my Sony smart TV's native interface is to go into settings and turn off WiFi. It isn't a dumb TV, but might as well be.