Functionally, all of these can be classified under the first option, "ET origin", because they all involve the revelation that some advanced intelligence unknown to the mass of humanity is active on Earth.
But there is a fourth:
* These craft are of natural origin
Some very strange analogue of St Elmo's Fire which results in the formation of metallic spheres of unknown composition in the vicinity of jet fighters.
> "These craft are of natural origin. Some very strange analogue of St Elmo's Fire"
"we humans are property of some more highly evolved beings that live in a realm that we cannot see. Those invisible beings are immaterial: they are made of energy and Russell compares them to ball lightning."
* From deep in Oceans
* From subterranean
* From millions of years in past
* From millions of years in future