Two points, Henrik:

First, the general term 'pyramid' includes tetrahedron. So, Robert is correct in describing the object as interlinked pyramids. Although, why the isometric magnetite crystal was invoked to compare to this object, I can't understand.

Second, I believe a stellated octahedron requires the two tetrahedra to 'interlink' to the point where the vertices are described by a cube. In other words, that object Thoth is holding is not interlinked enough to be a stellated tetrahedron.