[sneak]

There is a physical switch. It's the lid. It's not even a soft switch, the article clearly specifies that it's done in non-reprogrammable hardware logic, which is immune to tampering even by Apple who has bootloader signing keys.

[notabee]

That's a pretty poorly designed switch, if your intention is to turn off the microphone while otherwise using the system. It's better than not having any way to disconnect the microphone, but strictly inferior to any system where you can toggle the desired state at any time.