If the “things” are believed to be have superior abilities compared to American vessels/craft, which country on Earth could have created them? Not China, and Russia probably not. Christopher Mellon (former Deputy Assistant Secretary of Defense for Intelligence) says he is pretty sure they are not US craft.
Mellon, Elizondo, and most of the pilots who witness these things have said that they are so much more advanced than anything we can imagine. They are certainly not ours or our enemies'.
As an aside, new technologies do not emerge (poof!) out of a vacuum. They are part of a process of technological evolution and development. We would have noticed forerunner technologies and would be able to extrapolate from those to these.
Israel is most advanced and has reason to keep secrets.
You answered your question