More than anything, it is a testament to the skill of CD Projekt Red. I wouldn’t call it a miracle since any game can be scaled to meet the capability of the hardware: you could get The Witcher III to run on PS2 if you have the discs and downgrade to do so. The game would essentially need to be remade in that case, but you see my point.
Having The Witcher III on Switch is a huge deal. It really shows how much developers are embracing Nintendo.