If anyone on this primitive planet had the technology to make a craft maneuver and perform like these did, standing physics on it's head, there is no way in hell it could be kept secret. Kinda of a no brainer.
It turns out that if you had the kind of technology that could turn physics on its head, you probably would also have some pretty cool stealth technology that could make your stuff appear and disappear to chattering apes...
As Terence McKenna used to say “We may not be the only tenant in the building...”
A simple question might help: “Do ants believe humans exist?”
If you are tempted to say “Well, ants are dumb...” that is your clue....
:-)