Is this a new dimension? Or have we just time-travelled, or could it be both..?

( ! MOSTLY CANON UP TO CHAPTER 6 ! )

Gabi was stampeding through the crowd, trying to get to the central region were Eren Yeager was, while Falco tried to keep up with her, until they both fell into a portal that took them into the walls were the 'Devils' lived.
Were they in a New dimension or have they just time-travelled, or could it be both..?