It says in the article why
The new game is a GPS based Action RPG with a new story that builds on the Kingdom Hearts storyline… While the new game isn’t an AR title, it does use a player’s real-life location to figure out their location in the game’s map.
Given that this is kingdom hearts and multiple worlds exist in that franchise and its possible to travel between them it’s possible to have 'travel the world without leaving your home" and still make it so that the full game is only playable with GPS location. All they’d have to do is tie physical locations to worlds in game but then make those worlds navigable without requiring the user to move.