There's a documented white paper about what it does and you can examine network traffic to determine if it's doing anything claimed. Even today, there are people that have flags and filters set up for traffic coming from these devices. I don't think there's much to worry about here but it's good to see that people are skeptical. People take their data for granted far too often.
In addition to real time encryption, it also handles sound and siri, which presumably involve some form of remote communication. I trust Apple as much as NSA, MacOS is closed but it's pretty controllable, T2 Chip is not.
He/She is just trying to be cute. The T2 is a security chip that, ironically (in the context of the parent,) makes spying more difficult since it's on-device security.