I tried playing around with an edit in post - and turning it off. The exposure was unchanged but the shape of the histogram changed with changes in the setting. Some areas of an image seemed to have no change, while other areas had fairly dramatic changes.
The tone curve being applied by Nikon is relatively complex - I tried to create a similar result and it would not work very well. You can apply a curve from a High setting to an image taken with Low. The effect is to brighten dark areas while maintaining the highlights and lighter areas.