Sandbox literally redirects to "Open World" on wiki.
The terms have been interchangeable for a long time now. Might as well get used to it, because this most likely won't change back.
Actually sandbox means every open world game or a game where you can have some choices made by your own. I know that sucks. I would really like that openworld games would somehow be divided from the true sandbox games like minecraft, dwarf fortress and garrys mod.
The sandbox term has been warped by game developers into roping more customers to their product.
Few years down the line, there will be divided tags for games "sandbox" vs "true sandbox" and it'll just get abused further by those scumbag marketing departments at game developer HQ.
If you don't have absolute control in one way or another in your gaming environment (terrain, combat and story), it doesn't deserve the sandbox tag.