A quick look at the gcode immediately shows that it's a series of line segments - there's a G1 near the beginning, then just a series of coordinates thereafter which will also use the implied G1. Not a G2/G3 in sight.

My guess is that the DXF you are exporting, for some reason, is using straight line approximations and not curves or arcs. I've had that problem exporting from Adobe Illustrator and it turned out to be that I was not using the latest available DXF format. Can you explore that?