Your TV could send telemetry via 3G - you’d never know. Or the manufacturer cuts a deal with your broadband provider and gets a backdoor out via your WiFi hub,

Your TV could send telemetry via 3G - you’d never know. Or the manufacturer cuts a deal with your broadband provider and gets a backdoor out via your WiFi hub, if you use the standard one they gave you. Or a hidden app on an Android phone that the Android TV chats to when it’s nearby. IP over HDMI is also a thing. I am never connecting our Sony smart TV directly to the Internet, like you we have an AppleTV but it’s only a matter of time before you won’t be able to buy an unconnected TV at all.