Subtle, but puzzling since they serve the same functional goal — input numbers. There’s no logical reason for the inversion if a user operates the interface in the same way. Common sense suggests the reason should be technological constraints. Maybe it’s due to a patent battle between the inventors. Some people may theorize it’s ergonomics.
With no clear explanation, I knew history and the evolution of these devices would provide the answer. Which device was invented first? Which keypad influenced the other? Most importantly, who invented the keypad in the first place?