It's probably the same as the 2x zoom in the iPhone 16 line. The 1x pictures are a 48MP sensor that does some pixel-combining to output a 12MP image. The 2x pictures are a crop of 12MP in the center of the sensor, that doesn't do any combining. So it's still "optical", but it's lower-quality than the 1x.
I think it's not "zooming with the sensor", but has a slim lens stack to enable optical 2x zoom. The whole system is also PDAF, so they need the movement anyway.
Optical zoom changes significantly how out-of-focus areas looks like. For anyone doing photography (with actual cameras and actual lenses), calling crop an "optical zoom" is a lie from Apple.
If you have an actual physical zoom lens, cropping a zoomed out photo produces a different result than zooming in with the lens in the first place. Even when your camera/sensor doesn't move. It's all physics yo