The U.S. military's declassified 42-second color footage shows a Russian Su-27 approaching the back of the MQ-9 Reaper drone and releasing fuel as it passes, the Pentagon said. Dumping the fuel appeared to be aimed at blinding the drone's optical instruments to drive it from the area.
My opinion/question/guess:
Dropped fuel will partially vaporize.
HOT EXHAUST from the passing jet.
I wonder why there was not a FIREBALL ? ? ?
Bekeart