It is way more likely that we have found ways to spoof items on radar/sonar/FLIR, and that would be crazy beneficial to the military. Think about some of the characteristics that have been noted. The Princeton saw 10-20 aircraft suddenly appear on the horizon at 80k ft. Within a second they were able to drop to sea level.

Known generically as an Expendable Active Decoy (EAD), each BriteCloud round can individually mimic the radar signature of the aircraft it is launched from, causing threat radar systems to track the drinks-can-sized decoy rather than the aircraft itself.

https://asiatimes.com/2020/10/test-of-raf-drone-swarm-seen-as-game-changer/