I have created a Civil Geometry Line using the Line Between Points tool.
The line only has two points on it, a beginning point and an end point. I have also applied stationing to the line. When I use the Export to Native tool under the General Geometry task menu I do not get a chain stored in my GPK.
Civil Geometry Lines that contain two points will only be stored as Points and Line elements in the GPK file as long as auto persist is set to true on the feature definition.
If you were to use the horizontal geometry tool, Complex By PI,
then the Civil Geometry Complex Element, consisting of two points, would be exported to the GPK as a Chain element.