Many people have "heard" this and repeat it as fact. Not a single one has ever provided a single shred of, trivially testable, evidence.

While I've certainly heard plenty of theorizing about the possibility of this happening, I have yet to see any conclusive evidence that it has ever been done.

EDIT: What I am referring to here is the specific allegation that smart TVs will connect to open wireless networks without being commanded to do so. It's not a catch-all for any nefarious thing involving TVs or wireless networks.

You still run the risk of a software update doing a tv to tv mesh network. You gotta own the software or remove the radio.

How many open WiFi networks are there within range of your TV?