i've got an alternative. these are us military craft, and classified. they won't brief public officials on their purpose or intent, because public officials aren't in the need to know, they're not cleared to know. that means the public itself isn't cleared to know either. if they were enemies, they'd have been shot down already. if the gouvernment knew what these were, they'd have shot the vehicles down already. trump alluded to this in that social post from a few days ago with his typical typos. that implies it's a domestic force, not foreign.
Netherlands