G-Code supports three movements, a line between two coordinates, a clockwise arc, and an anti-clockwise arc.
You need to do the extra work in Rhino so only lines and arcs are exported.
The CAM Imperial and CAM Metric DWG/DXF export schemes have the export settings fixed.
However, before you save it out, you need to convert the curvy line (not lines, circles, and arcs, but everything else), to chains of arc segments.
Use the Convert command to make arcs. Set the Angle tolerance to zero to disable it. Then use the Tolerance to control how far you are comfortable with allowing the chain of arcs to pull away from your NURBS curves. The dots on the preview will show you the arc it will replace your NURBS curve with.
The problem is if you don’t convert to arcs first, Rhino NURBS curves will be approximated with short, straight line segments that approximate the smooth NURBS curve.