The interpretation that the poet’s description of his aunt supports is:
The poet feels that the public perception of the war is inaccurate and that the reality is much different.
This interpretation aligns with the lines that suggest a disconnect between what "everybody was fighting for" and the poet's view of the war, indicated by the casual tone in the reference to his "sweet old etcetera." The poet seems to convey a sense of irony regarding the earnestness with which people view the reasons for war.