They surely don't describe it as a sandbox on the official website more like an open-wide world building game:
The sandbox term is being used in all kinds of ways nowaday.
to define sandboxes. if 1 person calls it a bird, question it, if 2 people, question yourself, if 3 or more, you sir, are either stupid or crazy
edit, if you love your pay 2 win sandbox so much, why don't you go play that instead of trying to tell us what a sandbox is, because, well, people who know gaming have called them sandboxes, because they're sandboxes. If it hurts your feelings because it's not pay 2 win, it doesn't matter because your feelings are irrelevant and on that note, my dinner is done, time to smash and then go play in the sandbox known as elite dangerous, where pay 2 win isnt an option, and you're probably stuck driving a sidey cuz u got pooped on and couldnt buy it with cash toodles