What does SQL Server do for spatial data outside the bounding box of the index?

Question

I read an article that says:

(x-min, y-min) and (x-max, y-max) coordinates determine the location and size of the bounding box. Space outside the bounding box is considered as one cell, which is numbered 0.

I took this as meaning that everything "outside" the index is actually indexed in a special place, so if I do something like:

SELECT * FROM GeometryTable WHERE @MyShape.STContains(GeometryColumn)

If @MyShapecompletely outside the bounding box, it should only scan objects outside the bounding box (therefore, it still uses the index).

But later in the article it says:

Only operations computed on objects that are completely within the bounding box benefit from the spatial index.

It seems the other way around: if it @MyShapeis outside the bounding box, it will perform a full table scan.

What is it?