It’s in the 2h long Gamersnexus video. The TVs aren’t connecting to open WiFi networks but connecting to other LG TVs within range. That forms some sort of mesh network that lets the TV access the internet. Apparently it’s not illegal wardriving because “they own the glass”.

The GN investigation discovered that LG makes the TVs mesh with each other as well. So even if you don’t connect your LG to the internet, it can connect with other LG devices in the neighbourhood and exfiltrate data that way.