"in a jetpack" is just a colloquial way of saying "wearing a jetpack". other examples of this type of language include: "Do you see that man in the suit over t

"in a jetpack" is just a colloquial way of saying "wearing a jetpack". other examples of this type of language include: "Do you see that man in the suit over there?" "the suspect in body armor was described as being 6 feet tall." "man in an orange shirt" is the title of a popular pbs show. etc etc etc.