Operative word; “Unidentified.”
Due to our sophisticated military sensors (particularly on Naval vessels and aircraft), we have a lot of information about what is being observed.
The DOD has stated unequivocally that the "unidentified" ones are not Russian or Chinese drones (though adversarial drones have been observed...and identified as such).
And now scientists at Stanford (Garry Nolan), Harvard (Avi Loeb), and other universities (as well as scientists not affiliated with univ labs) are getting into the act.
The word "unidentified" doesn't mean "nothing is known."