So you feel that this explanation is less likely than aliens?
The source being terrestrial is most likely. However, it cannot be tech from our civilization because of what it is capable of. We cannot build aircraft which can handle those forces and accelerate like that yet due to engineering constaints, so it being ours is less likely than anything else by default. It's as impossible to build for us now as a cellphone would be for the ancient Egyptians.
Again, I don't like people strawmanning any unconventional explanation as "aliens". That is a tactic of ridicule which has been used by the IC for decades to color the populace's perception of the UFO phenomenon. There are simpler terrestrial explanations which fit the facts, like a more advanced parallel/breakaway human civilization.