Looks more serious than just a terminal dump. CNN's banner is now saying "Authorities are not allowing any flights to take off or land at New York's LaGuardia Airport after taking man into custody, police say." And checking some AA flights to ORD, a bunch have been cancelled and the rest delayed (those are leaving from D, not C) and there's a ground stop to LGA. It appears that AA398 is about to land, though.