The given rule "68-95-99.7" specifies that perhaps the breadth around one standard deviation across each edge of the partition covers 68% throughout the area.
Furthermore, the breadth of two standard deviations across each edge of the boundary covers 95% throughout the area.
99.7% of something like the region is protected by that same side of three standard deviations along each partition side.
Consequently, because the shaded region encompasses the range of two standard deviations, the portion protected is 95%.
