CIA/Pentagon/White House workers have lives. When something big goes down like ....oh I don't know....Iran getting spicy and launching hundreds of drones and missiles at Israel overnight, those lives get disrupted.
People work overtime and order takeout or aren't able to go out on the town like they normally would so that makes changes to the usual data patterns in the DC area. So they say ramp ups in US military activity can be predicted by detecting those changes.