If I had to guess, I would imagine their workflow went from ArchiCAD to Maya to Rhino to ArchiCAD.
The article mentions ArchiCAD and Maya specifically but I've read elsewhere where they mentioned Rhino as well - and it would make sense since Maya is not particularly good for producing fabrication data.
I think they built the context (site) in ArchiCAD along with the basic 2D Layout information for the final sheets, and then used the basic context massing to proportion and act as a base in Maya where the actual undulating form was modeled (using either Poly/SubD modeling or Maya Nurbs modelling) and then the non-sliced form was exported to Rhino where it was cleaned up and then sliced using either a Grasshopper definition or Rhino-scripting to spit out Nested 2D profile or contour curves that could be annotated or numbered and outputted for CNC milling or routing.
At least that's the workflow I used myself when I worked on a similar project
I doubt they re-imported the sliced model back into ArchiCAD (too many polygons for ArchiCAD to handle) but I could see them re-importing the finished Maya model (pre-slicing) back into AC as a "dead" or static geometry for use in their documentation for permit application and site-placement.
They might not even have had to do that as long as they would have been able to extract 2D curves describing the contours of the overall form in plan and Elevation (section) and exported/imported those as DWG or pdf format.
Given the timeline, it's also highly unlikely they used anything later than ArchiCAD 13 for this project since it goes back almost 2 years long before AC 15 was even in Beta (I imagine).