It's interesting to see other people's definitions of words. For me, the difference between a declaration & a maneuver is one of PC agency. A maneuver is something your character does. A declaration is something that a player does, to establish some truth about the game world.
So, a maneuver of "The building is on fire", is your character committing arson.
A declaration would be a player saying something like "Hey, those cultists summoned a fire elemental, right? I'm going to make a lore declaration that they set the building on fire." Or perhaps, "Wait, we're fighting Harry? The building should probably be on fire by now..."