This is because they rooted the TV.
They can just start a capture, record to RAM / storage, and retrieve it later when it is reconnected to the network.
Otherwise if it's disconnected, it is still hard to exfiltrate the data somewhere. Maybe they could get creative via Bluetooth, but then you would need a cooperating device in proximity of the device.
I think the main risk is that if you - or your kids, or your spouse, or a guest, or someone you give/sell the TV to - do connect the TV to the Internet for even a moment years from now, then all those logs you wanted to keep away from LG are likely to delivered.