Hello, dear reader, your question is actually quite interesting!
Despite often being conflated in casual conversation, ‘shipment’ refers specifically to the process of delivering goods, in contrast to ‘cargo’, which refers to the goods themselves regardless carried on a vehicle, aircraft, ship, or automobile.
Etymologically speaking, 'cargo' comes from the Spanish noun form of 'cargar (v)' meaning 'carry/lift something as a means of transport' or 'to load (a firearm.)', which itself is inherited from the late Latin word 'carrus (n)' meaning 'a wagon or wheeled baggage cart', initially referring to the things carried on such wagons and incidentally sharing the same lineage with the English word 'car'.
While 'shipment' unsurprisingly coined from 'ship (v) and -ment (making it a noun)'. First applied to transporting goods via ship, its meaning is later expanded to mean the process of transporting goods in general (understandable as the main mode of large scale logistical transport from the beginning of human up until the advent of steam power relied predominantly on water routes)
As carts and wagons are open air museums to their relatively small and simple load, the holds of ships is a zoo of different stuff that possibly share nothing in common except their destination, people ( ... ...probably ) got tired one day of playing draw-and-guess with what is keeping their wheat company and reserved ‘shipment’ for the process of shipping, only delineating between the stuff that is shipped until they can be seen unpacked on the back of wagons as ‘cargo’. [Source Cited from George & Jonathan]
Thus, the process of delivery made by car would still be called a 'shipment', and the same principles apply whether it be a cart, wheel barrel, motorcycle, bicycle, unicycle, tricycle, rickshaw, helicopter, car, Wuling Hongguang, desert purpose Honda tachankas, Panzerkampfwagen V, T-34, Sherman 4, T-34, tractor, hearse, ambulance, airplanes, the DC-10, windmill, horse, horse rider, dog, L3/35, rabbit, spherical cow, sea cucumber, the titanic, can-opener, mass-less volume-less point in space, car, railroad, railgun, caravan, balearic slingers, trees, submarines, particle accelerator, broomstick, ballistics of a boomstick, hot air balloon, cold air hydrogen balloons, a colder von Hindenburg, car, centrifugal force, free fall, matrix addition, and in some exceedingly rare and generally obscure instances, perhaps even ships. (non-exhaustive list)
Best,
Dear Letterbox