It is difficult, if not impossible, to tell. It is a matter of perspective. If you move, it can appear that the other guy is moving towards you. So in this edited video from the Chinese, who can tell who was actually making the 'sudden' maneuver? In flying, you always have slight amount of drift. You or the autopilot system will constantly correct, but drift always occur. A clearly visible maneuver is when you see an attitude change, evident by the wings. We do not see it in this video, so it is difficult to determine who maneuvered.