Yeah, its some sort of patented quick disconnect.
Wish I could find an aftermarket stem with something similar. If I there were a way to have a quick disconnect like this, even if it was only for the rear brake cable, I could make an aero roadbike like a Cervelo S3 or Felt AR work double-duty as a TT bike with very little compromise. With a 2nd cockpit (maybe with 2nd front brake attached), second TT-oriented seat post with a TT saddle, one could do the swap in ~10 minutes. If you wanted to get real fancy, you could have a second, higher-offset fork from a smaller frame size for more front center.
"They're made of latex, not nitroglycerin"