Nothing to do with NPUs, as far as I know, it's down to the dedicated video stream acceleration that ARM chips have carried for a while.

In practical terms, Windows Hello unlocks noticeably faster, just like a phone with facial recognition does. It also disproportionately handles video playback more efficiently, given the relative overall performance. Nothing new, either, it's all stuff Apple got out of their own ARM transition, but way underrated in how much of a moment-to-moment difference it makes, particularly for stuff like the Surface Pro and other hybrids, where you want to handle it on battery and use it more like a tablet sometimes.