It doesn’t matter what he said. What matters is what he signed.
1. That’s not entirely true-Presidents are held accountable for their signing statements, and good lawyers would probably even find ways to use those statements to help prove something in a court of law. They mean something if said president wants to keep any hope of reelection and keep himself from being impeached and ensure his political career doesnt get ruined and supporters turn on him and the whole Democrat party-which ideally they dont want.
2. As said before, he didnt sign anything that clearly and unambiguously gives the govt any more right than they had already to detain someone without a due process. Whatever power the govt has now to do this, they’ve always had.
So the signign statement does count for something. Of course the question is how much it counts for.