Probably done to detail the car to resell it. I used to do work for dealers back then and I bought the stuff by the gallon. It was a popular way to freshen up the trunk.
Certain 60s Mopar were factory splatter painted, depending on the plant where it was built. I had 2 '66 Satellites, one was splatter, the other was body color. Same way with some other B-bodies. I also have a '70 Polara that is splatter painted.
Dallas