UFO spotted by flight instructor and student pilot over San Diego. ATC confirmed no radar contact.

UFO Spotted by Pinnace Aviation Academy training aircraft Green/White Cessna 152, tail number N4711B on 6/13/2021 around 4PM local time. Tail number N4711B was crewed by myself, a flight instructor, and a student pilot. Our flight level was around 3,500 ft MSL level over Bonsall CA heading northbound after leaving Palomar Airport (Airport code: KCRQ, our training base).  See flightradar24 for tracking information.
 Spotted the UFO over the city of Papa, directly over the Pala Casino around 2-3,000ft MS, low flying over the mountains. No radar or communication contact in that area. UFO was shaped circular, the size of a small general aviation aircraft, color was black and silver. The UFO was spotted by both crew members.
 The UFO was turning towards us (southbound towards Bonsall, CA) traveling around 90-100knots. Then the UFO seemed to be stationary or moving slowly 30-50 knots at same altitude as us (3,500ft MSL) as it passed us on our right by about 500 yards. I initially thought it was a balloon but then the object increased its movement to around 400 knots and greater southbound towards Palomar Airport (KCRQ). Object travelled faster than any conventional aircraft or even military aircraft except for high performance jets, however the object was smaller than an F16 fighter jet.
 As the object travelled from by 3 oclock to 5 obclock position releative to our airplane heading. The object changed to different altitudes and headings along its route southbound while it was fast moving.
 Contacted Palomar Airport to ask for any secondary radar over Bonsall Area where the UFO was located. ATC confirmed no reported secondary radar aircraft in that area.
 Possible military UFO (more than likely drone) due to the recent San Diego military exercises off the coast of San Diego and the report sightings made by Navy personnel. Recent sonic booms reported a few days ago over San Diego.