I don't doubt the guys story, its believable. As far as the improperly assembled armor, how many times have we seen stromtroopers incorrectly dressed in the films. Being an extra in the background, it stands to reason that his costume was thrown together to look right from a distance and intermingled with other troopers.
Additionally he states that his costume was said to be used in tunisia so the incorrect shoulder straps and lack of drop boxes only support his story.