Yes, it's true that the app could hand-track "recoil", just like it's seemingly tracking his gestures in the 3D GMail.
I still think it's staged. The motions look way too "casual" and not deliberate enough to be interpreted easily in software without some revolutionary tech, in addition to the unrelated revolutionary tech needed to do the AR "live".
Try it really quickly. Hold your hand in front of you like you are holding a gun. recoil your hand. feels pretty cool, right?
Now, just imagine that the software is tracking your hand and the gun shoots whenever you intentionally recoil.