Both, and I guess Kicad takes the bigger share.
Try to save in an older dxf-format and than import into Kicad.
Attachement saved as DXF-R12-format in QCAD and imports without error-message into Kicad. outline_v2_r12.dxf (22.2 KB)
The root-cause is that DXF is an ever changing/enhancing format. For instance QCAD (similar to librecad) alone offers me 7 different dxf-versions during file-save.
So I think your outline.dxf contains elements from a dxf-version newer than Kicad can import.