no, it is a kicad import dxf limit, that can be found at the manual
http://docs.kicad.org/4.0.5/en/pcbnew.html#_creating_a_board
6.1.2. Using a DXF drawing for the board outline
As a first step, any POLYLINES need to be split (Exploded) into their original simpler shapes. In LibreCAD use the following steps:
- Open a copy of the DXF file.
- Select the board shape (selected shapes are shown with dashed lines).
- In the Modify menu, select Explode.
- Press ENTER.
From your FC setting menu you have Max Spline segment to 5mm…
Move this setting to 0.01mm as suggested by @Joan_Sparky to be able to export correctly also complex spline (which is not your case atm).