This. It fits a lot of aspects of past "UFO" sightings that were actually just a reflection. The major issue in this case is multiple witnesses, and also supposedly multiple instruments detecting it (I've seen this claimed in comments but not the evidence itself)
If the thing behaves as though it has no inertia and does all these amazing movements, what else does? A reflection or otherwise illusory object can do all that easily, in fact thats the default behavior.