Why does one loft create a polysrf and the other a surface

[Lagom]

I have no idea how you created your curves. I never use arcs in my field of work. I only do traditional NURBS surface modelling and must avoid curves with kinks. Maybe this is useful:

@davidcockey

A user can transform an exact arc which is a rational degree 2 NURBS curve into an exact rational degree 3 NURBS curve using ChangeDegree with Deformable=No. The degree 3 form of an arc will have multi-knots even though curvature is continuous.

@jeremy5

Rhino identifies a degree 3 arc as a “Nurbs Arc” as distinct from an Arc

@pascal

NURBS arcs in Rhino are indeed made as degree 2 but what makes them shaped exactly is the control point weighting. You can ChangeDegree to 3 but these curves will still be rational.