Spurious data glitch on ADSB you sometimes get ground stations showing ridiculous altitudes.
Not the first time that the helo has flown sorties around DC area.
Link here to story June 2nd 2020.
https://www.thedrive.com/the-war-zone/33817/nuke-sniffing-helicopter-flies-around-washington-amid-protests
The helicopter in question, a Bell 412 that carries the civil registration number N411DE, is one of two that are part of the Aerial Measuring System (AMS), which also includes a number of specially configured Beachcraft King Air fixed-wing aircraft. The National Nuclear Security Agency (NNSA), the division of the Department of Energy responsible for overseeing the development and production of nuclear weapons, manages the AMS program through its Remote Sensing Laboratory. Elements of the AMS are based at Joint Base Andrews just outside Washington, D.C. and at Nellis Air Force Base near Las Vegas, Nevada.