MultiPolygon features behave like a single Polygon feature. You cannot create a non-planar polygon. Every ring of a polygon must be planar and all parts and all rings must be in the same plane.
Creating a new MultiPolygon feature.
A polygon has one outer ring and can have one or more inner rings. A ring within a polygon is considered a hole. To create polygons with multiple outer and inner rings, create a MultiPolygon feature.
You can create a feature that includes arcs, even if the data store for that feature class does not support arcs. In such cases, you can set an option that determines how the arcs will be segmented when they are saved back to the data store. See To Set Arc Segmentation Values.