Fort Dix, which is an airforce base, is in New Jersey. Wouldn’t be surprised if it was them. There was an incident some years ago when a very strange supersonic noise blasted out from that area and the government was very quiet about it.
I haven't been highside in almost a year now so I don't purport to know the actual operation behind this, BUT I would place my money on testing surveillance systems and on-device tracking modules. CDAO has been investing very publicly in these areas alongside the Maven program and TF Lima. They need a lot of good data on populated areas to make this work; they also can't risk testing this in warzones where a downed drone will both [1] leak advances in technology we have made since Reapers and [2] expose the on-device models they have in place. Could even be a vendor trying to evaluate their models; there is nothing particularly illegal about these drones.
I'd just like to interject for a moment. What you're referring to as Fort Dix, is in fact, Joint Base McGuire–Dix–Lakehurst, or as the DOD has recently taken to calling it, JB MDL. Fort Dix is not an army base unto itself, but rather another component of a fully functioning tri-force base hosted by the Air Force and including units from all six service branches.
