In many cases, the full circumstances of an event make the difference whether a law has been broken or not.
Were there any license requirements for things like flying the drone, owning the gun, firing a gun from a flying platform? Was that drone allowed to carry any cargo?
Where did it happen exactly? It may make a difference whether it's private land, public land, a gun range, or maybe a nature reserve.
It is not that black and white. So many possible questions may be raised which may determine that an act is legal or illegal.
Example. If you see something happening, it may be legal, it may be not. If you see a house being built, you will probably assume it's legal for those people to build their house there. But maybe it's not. Maybe on that piece of land, nothing is allowed to be built. Maybe they don't own the land. Maybe the building is not up to code. Maybe it's bigger than allowed. So many circumstances where building a house is legal, so many circumstances where building a house is not legal.
Another example. Grabbing a gun and firing it is, afaik, in general legal in the US. However doing so a busy street I suppose not legal. Aiming it at someone and then firing it, is also usually illegal - note the "usually", there may be moments it is legal, and then again it matters whether you're say civilian, military or police.