It's interesting that Colt retained a product name developed by ArmaLite; it was certainly early enough in the game for them to call it whatever they wanted and "reinvent" the rifle if they desired. I guess the suits at Colt liked the original name and thought it would sell (and they were correct).
I always figured that they thought it would be nice to go along with the “Colt Automatic Pistol” and the “Colt Automatic Shotgun.” None of which were actually designed by Colt.
Technically, both “Automatic Rifle” and “ARmalite” are correct answers. “Assault Rifle” is not. :P