If TFA is to be believed, his craft wouldn't meet the requirements of an ultralight aircraft:
103.1 Applicability.
This part prescribes rules governing the operation of ultralight vehicles in the United States. For the purposes of this part, an ultralight vehicle is a vehicle that:
[snip]
(e) If powered:
[snip]
(2) Has a fuel capacity not exceeding 5 U.S. gallons;
From TFA: According to court documents, Hughes rented a car and towed his gyrocopter from Florida to an airfield in Gettysburg, Pa. He chose the location for its proximity to the Capitol -- about an hour away and reachable on the aircraft's 10-gallon fuel tank -- and the fact that it was an uncontrolled airport, according to a criminal complaint.