If I recall, the AT-4 waas Swedish-made, and consisted of a launcher and an 84mm (some say this is where it got it’s designation, from the size of the warhead) High-explosive-anti-tank (HEAT), shaped charge round, and had a range of 1,000 meters. The US Marine Corps (and the IDF) referred to the AT-4 as “the Bunker Buster”.
If it was found on a lawn in New Jersey directly across from Manhattan, it was most definitely found in a spot which sits astride, or dead-on, the flight path to Newark (Liberty) International Airport.
Perhaps some of our Muslim friends in Jersey City (where they are legion) training for a potential attack on an aircraft?
Something to look into, i should say....
P.S. That is NOT to say that this does have a terrorism angle, just that it is a possibility.
It’s also quite possible that someone brought this home as a souvenir from a Reserve weekend or something and just decided to ditch it, or forgot about it.