My best bet...
Officer Friendly looked in the AZ code book for discharging firearms, unlawful.
Using his comprehensive skills, he noticed that although there is a section for "...In self-defense or defense of another person against an animal attack.." but no corresponding sub-section regarding defense against humans.
(link provided by author)C. This section does not apply if the firearm is discharged:
1. As allowed pursuant to chapter 4 of this title.
Such a tiny thing, you can hardly blame the officer for missing it, really.