I believe he's referring to extruding a closed shape, either with extrude, or using Shell modifier.

If you create a circle, for example, and add a shell modifier, with thickness, you create an extruded shape, with caps on the top and bottom.  The caps would be Ngons, because closed shapes are just outlines, and have no inner space to get converted to polygons.  So Max does the most efficient thing; it caps the ends with ngons (the extrude modifier has the option to cap the start and end of a closed shape).  Lowering the interpolation of your shape will result in fewer vertices (and edges) in your extrusion, and make it easier to connect the vertices around the start and end borders.

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