In some of the threads about Sandbox campaign devolve into shouting match over whether it is was the default style "back in the day". The short answer of course not. RPGs are very flexible including the first version of Dungeons & Dragons. Very quickly RPGs campaigns grew in diversity once the game spread beyond it's minature wargaming and upper midwest roots.
However there is a reason for the "Golden Age" aura that surrounds the use of the term Sandbox.
Wargames have several ways they can be played. One is that you start with an order of battle, and a large scale map. Both side maneuver and where opposing forces come into contact a battle is fought using a smaller scale map. This style of wargame is called the campaign. And it shares many of the characteristics of a sandbox both RPG wise and Video game wise. There is little constraints on the player's actions other than the limits of the map. And sessions solely devoted to resolving individual battles. Sounds familiar?
More so than miniatures the campaign has proven to be the most enduring legacy of Roleplaying's wargaming roots.
It is also the source of the confusion over sandbox campaigns in the earliest days of D&D. But the connection is over hyped as RPGs campaigns quickly grew in diversity compared to their wargaming counterpart.