Thanks, Chad.
I did go through the tutorials so I thought I knew the definition of a polysurface but somehow I got confused when it came to this issue. For example, I know that a polysurface is a collection of joined surfaces such as the six surfaces that make up a box.
What confused me is that I was thinking of a polysurface as a solid but forgot that they can also be open. If I extrude a curve that is a single continuous curve or one line then it results in a “single” surface because it can be represented as a single mathematical formula. But if my curve has a combination of curves, or lines and curves, then the surface extruded from that curve would be a “poly” surface because it requires more than one mathematical formula to define.
I think that’s how it works. 