This is not at all what they did here. Here, they use the IMU sensors in the phones, not the cameras. Using cameras is too restrictive if one wants to apply it to more real-life-like situations due to visual obstruction etc. They are not the first to use pose and movement estimation using IMU sensors by any means, but I guess it still is a valuable contribution to have a working-out-of-the-box app, and also they seem to get into estimating more details in the pose than just a general classification.