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.