My guess.
Because "they" are the ones talking about it more than the people, it's probably a fabricated presentation with an agenda.
They belong to the US. They want to stir up some story to prevent Trump's inauguration. Maybe, there'll be a false flag event like an attack on the US, something terrible like a missile strike, then the military will blame some other nation and they'll try to cancel out the inauguration and the weapon makers will make another set of billions.
The drones are said to be very large and can have extended flight times. Probably from a higher battery capacity. Maybe they run on fuel.
They want to be seen, but not really, so they only come out at night it seems.
It's been reported that people are unable to fly their camera drones to take a closer look. Normal drones usually have this software in them that'll prevent them from flying in no fly zones, I imagine when the UFO drones are out, they implement the DJI Flysafe system that prevents people's drones from taking off.