Were they hired by a human resources person with a predilection for people of shorter stature?
Is being vertically efficient a bona fide occupational qualification for working in a copy shop? As a person of above-average height would I be refused a position if I applied to work there based on the grounds that I would have further to lift when I moved boxes of paper and further to bend when clearing paper jams out of the copiers increasing my chances of accident and personal injury?
At one time, were they taller but prolonged exposure to bleached paper, photocopy toner and ultraviolet rays somehow conspired to gradually shrink them?
Occam's Razor tells me that the simplest solution is usually the best. Could it be nothing more than pure coincidence? Or is there something else going on?