When they first announced it 2 years ago yes they said it would use the same Hyrule from BOTW but years after the first game. The idea being they put so much into it they could reuse in some ingenious way and still make it feel fresh. So since then there’s been speculation as to how they’ve changed it. Underground areas? Underwater areas? Or rebuilding all the towns that were destroyed etc…
Then, we all thought that would lead to a fairly quick turnaround, like Majora’s mask after Ocarina. But it’s actually been quite long. So either covid massively slowed them down, or they’re putting a lot more into it than we thought, or a bit of both