Looking at their overview, this is Constructive Solid Geometry rather than B-rep (Boundary Representation) solid geometry. STEP does hypothetically support CSG, but B-rep STEP files are vastly more common in my experience.
I'm not sure how useful this is to you but there is an OpenSCAD workbench for FreeCAD. [0] In theory you should be able to export STEP files via FreeCAD.