It's probably regular airplanes, stars, and Venus, and now, I assume civilian drones. Once people started claiming drones, other people who never bothered to look in to the sky started seeing lights they didn't understand (planes, stars, planets) because they never bothered to study the night sky in even a basic way, and they are suggestible. Then people probably started flying their own drones to do investigation + prank people.

+ StarLinks or other low orbit satellites and space stations. In 2014, when Russian invasion started in Ukraine, we had so many reports from folks about drones in the sky about ISS or Venus. I saw this myself when I was at Chongar, near to Russian occupied Crimea: my comrades pointed to bright Venus in the night sky and said that it can be a Russian drone. I dismissed the claim by pointing out that army doesn't turn lights on when on mission.