I’m using an Apple TV that is connected. My prior setup, with a newish but unconnected Sony Bravo, the remote just passed mic audio data to the Apple TV as if I was using the Apple TV remote

Also, pretty sure it’s undocumented, but I’ve been on a handful of reddits and HN conversations in the past where people are all experiencing this. I think a simplified theory is that they broadcast the WiFi credentials over Bluetooth and other unconnected devices can then get online. I remember one discussion of this theory where the guy found out his TV had connected to his neighbors WiFi somehow and this was a theory in the thread. It’s foil hat type stuff but very believable if you’ve experienced having devices know your WiFi despite having never granting it.

Another theory is similar where the unconnected devices send the connected device data to relay. This would allow the unconnected device to remain stealth, as it wouldn’t appear in your WiFi logs. There’s even a deeper level theory on this one where devices (particularly cheap Chinese toys and gadgets) come preloaded to exploit common vulnerabilities in other devices to establish this relay. Imagine a smart oven or fridge where the manufacturer has no incentive to keep up the firmware for security purposes. So now you have a baby monitor sending data to China through your air fryer’s WiFi connection.

Those are indeed tinfoil hat theories.

There's no protocol for that over Bluetooth. One could be created, but it hasn't been yet. Nor for relaying data. These don't exist. Like, there are limited relays like what iPhones do for AirTags, but not for a vacuum cleaner to transfer data via your fridge to your neighbor's open WiFi.

In every case where someone's TV has mysteriously connected to a neighbor's WiFi, it's kids or the babysitter or someone else who actively tried to connect to watch a show.

I think you’re probably right but I just wouldn’t say it as confidently as you do. There doesn’t need to be a specific protocol if the manufacturers are in cahoots (and there’s plenty of reason for them to be) they make their own and obfuscate it amongst all the other things these devices do.

I'm confident because Bluetooth communication can be captured and viewed. It's not hidden. Nobody has found this. It doesn't exist.

So maybe it's not BT, that was only an example theory. It also doesn't need to be always running, so could be harder to track. What if it turns out it's just some high pitch inaudible sound using morse code... I could go on but I'm not trying to crack the case - my point is that things like this that you assert don't exist, often do to turn out to exist on a long enough timescale. I remember reading a lot of tin foil hat theories on various things that some people asserted were illegal or simply impossible; then a decade later Snowden proved the theories right. It seems like these things happen regularly these days.