Motion involves a transition from a prior condition to another. A particular movement was once absent, then occurred, and later ceased. That supports the origination of that particular motion.
A body's movement from A to B need not be the very same movement throughout all past time. Particular transitions begin and end. Yet the conclusion that the whole succession of motions must have a first member requires an additional argument.
The difference is crucial: “every individual movement is originated” and “no beginningless succession of movements is possible” are distinct propositions.