There are real videos, even months old of exactly these 'land drones', equipped with good ol' .50 cal. In certain situations, they fought extremely well given no risk for crew. I mean killing off entire bmp-something transport including all crew with AP rounds, typically during night since it has night vision, zoom and so on. Verified also by drone flying nearby.

Now I am not claiming all the facts stated in the article are verified by me, but I can imagine one of them got so lucky with drones and getting hidden from their view for prolonged time it could theoretically pull it off. Not sure about batteries/fuel/ammo part thought.