Awful lot of assumptions there. Is that thing an object? Maybe. Did that object travel the vast distances of space? No way to know. Drones? USAF isn't saying.
Conjecture 1: If the thing in the sky is objectively an object, and it's manmade, then no sane military-industrial manufacturer is going to tip their hand to the enemy. Safe bet.
Conjecture 2: If the thing in the sky is objectively an object, and if it is not made by man, then it is made by something other than present day humans. Also a safe bet, but odds are diminished.
Conjecture 3: If the object is made by something other than present day humans, then what are the likely of these unlikely options? Aliens? Time Travelers? Interdimensional thingy whatsits? Demons? Angels?
SubConjecture A: Demons or Angels? How do you even show evidence for that? Witness testimony. Not a safe bet.
SubConjecture B: Interdimensional thingy whatsits? Not sure how you would present evidence for that? "MIST" creatures crawl out of CERN? Not a safe bet.
SubConjecture C: Time Travelers? I guess you could build a quantum/ quantum- entangled computer that would transmit information back to the time of its original creation so that current people could get future tech blueprints with which to build, but I don't thing we're there yet, and that doesn't explain strange "objects" in the skies in prior decades/centuries. Not a safe bet.
SubConjecture D: Aliens. So far there's no evidence of life anywhere except Earth and low Earth orbit. Still, the ingredients surely exist all over the universe.
Extraterrestrial Hypothesis: If alien life exists, and if they have developed advanced civilizations, even millions of years ago, the speed of light is the speed of light, and it's highly doubtful little Glrxix would jump into a little saucer and cross the vast distances of space in one. Odds - no way!
Aliens take a mothership here and only use their little saucers and triangles as local shuttles. Still a long way to travel. How do you sustain a crew over thousands of years? Not a safe bet.
Aliens create and program AI self sufficient as to be self replicating. They could build sub light probes that could carry the source alien's DNA samples along with anything else they need to start terraforming (alien forming) planets or monkeying with the local life to make the alien DNA better suited to the target planet's biosphere. Birth them in tubes and let 'em go crazy with their new planet - just buzzing around in their shuttles and checking in on how their hybrid experiments are going. So while the AI probes could take thousands of years to get to other stars, AI don't care. AI goes to sleep except for course corrections and little nibbles of energy here and there. Not a safe bet, but of the ETH, the most probable of the improbable in my opinion.
A reproducible mechanical AI probe with some sort of inexhaustible renewable energy source which due to mass density equations could travel no more that 20% the speed of light is simply not at all likely to get from there to here. The distance of 100 light years is unimaginable.Then again not a bad thought however unlikely the postulate.
You touched on the likely answer a bit, but dismissed it.
After spending far too much time trying to separate the grain from the chaff, I am coming to the conclusion that there is more of an interdimensional aspect to this than one of physical 3 and 4 dimensional travel.
It explains much. A small craft would not have to travel interstellar distances. Things apparently appearing and disappearing could be phasing into and out of our dimension.
I am not saying it is so, but it is more credible to me than traveling 1000 light years to get here.