Explanation:

The doubt here is that the single body denoted by the word ‘this’ may mean the body of Arjuna and not of Krishna. This possibility is rejected because in that case, any of the above two options [1] would have been used so that the body of an ordinary human being becomes the reference. When an ordinary human being stands here by any of the above two options, naturally the body of Arjuna is also covered since he is also one among the ordinary human beings. Since the above two options were not selected, the body referred here must be the body of Krishna alone, since Krishna alone is a special human being, being the Human Incarnation, who is different from all other human beings.

[1] ‘The body’ or ‘every body’