It’s about as likely that the transistor is attached to a pin that sends an interrupt to the processor and it then applies a soft mute as it is the transistor is attached to a flip flop or register that toggles the mic getting power physically.
My guess would be it’s controlled by software rather than directly by the hardware because then they can do whatever they want with the button via firmware or software updates. This includes nefarious stuff like a fake mute mode, or more innocent stuff like special behaviour on a long press vs short press.