I remember a viral video that went around where a US general pretty explicitly said it’s “not terrestrial technology” or something along those lines. But you’re right, that also leaves open the explanation that it is terrestrial, just not technological, so I guess they haven’t explicitly admitted that. I also remembered the government had said that UAPs had played with and disabled, then reenabled US nuclear infrastructure in a way that seemed intentional during the Cold War, but I looked it up and that claim only comes from one guy who used to direct the DOD’s UAP observation program, not speaking on behalf of the government. Still, the way that they react to our aircraft pretty cleanly eliminates for me the idea that there’s a non-technological explanation for all of them.
There’s mountains of proof of inexplicable, seemingly intelligently-operated aerial vehicles which match no known human configuration and are thousands of years beyond our capabilities technologically, but no, no actual proof that they’re operated by aliens. But to be honest it seems a bit dense and almost intentionally obtuse to insist it’s more likely that they’re not aliens, since the only other explanation is that there’s some government or corporation on Earth creating aircraft with no discernible means of propulsion, capable of breaking the sound barrier without creating a sonic boom as well as accelerating and decelerating to and from very high velocities in a matter of seconds.