Rhino lines to AI workflow doubt

Hi. I am trying to help a colleague to continue working in a project that an old colleague prepared.

Basically, we need to export lines to AI. I am not sure how my colleague did it, but when he exported it, the lines come to AI as a closed shape. I am used to do the line export, but I always need to create the closed shapes before exporting, meaning that I need to rework my Make2D to have a closed shape for each section that I need to fill in AI. He solved it, I am not sure how, but he exported it, and then the shapes are closed in Illustrator.

Is this possible? Or he actually did the re-work without saving it in Rhino maybe, and then it looks like he exported it as closed shapes in Illustrator.

Thank you a lot.

Hello - CurveBoolean may have been part of the process.