I asked a friend about the Quantico flights. He was Air Force and an air traffic controller at MSP in the 70's and 80's. He said Quantico is a military installation and a private plane cannot just land there unless it's an emergency and no one has 4-5 emergencies in a month. He said they'd have to be granted special clearance from pretty high levels and be a VIP to do that. He even looked it up to confirm that Quantico is still all military and hasn't had any allocation to private aircraft. So… Could be a VIP.