Well, If they've got advanced tech, they could be observing us. And, keep in mind, shit happens. If they've got cloaking mechanisms, maybe systems were fried by something. Perhaps the vapor trail disturbance at :30 is the establishment of an atmospheric field of some sort (perhaps the environment isn't contained entirely on the ship, and instead bubbles outward. A failure in the containment mechanism could cause the gasses to shear off and become visible, depending on what they are. Maybe the hull ruptured and started to leak atmosphere.)Hell, maybe they had engine trouble and the wave is them kicking in whatever sub-light engine they'd need to buzz around quick enough to get anywhere in a solar system. The time they spend still visible after that could be them simply calibrating the repairs and testing their integrity. I can't imagine anything worse than your engine suddenly flipping you the bird and flopping in the middle of empty space.
This is all assuming it is an alien spacecraft. My thoughts.
Assuming it's a military craft, WTF China?
Yea. I couldn't not give my two cents on this. Awesome possibilities.