They also worked with equilateral triangles, cubes, etc. If one is about to analyse the crop formations, than you have to start with simple things. The most simple thing in three dimensions is the tetrahedron. It is the platonic solid made up from 4 equilateral triangles. But this object exists in three dimensions.
Crop circles are two-dimensionsal.
So we must bring something from three dimension into two dimensions. The world we see is made up from 3 dimensions. But everything in this 3D-world is acting from the energy of the higher dimensions. Physicists are saying that everything that is rotating gains its energy from the fact that it is rotating in higher dimensions also. And the higher dimensional rotating is letting some energy flow through the tetrahedron in the three dimensions.