As I recall the wind tunnel company had a FI model lying around and when Lotus came for testing they thought they'd use the FI model as a base for building the Lotus model. You can see their thinking, why build a model from scratch when one is lying the corner? All it takes is to change a few parts here and there.
More on that here:
viewtopic.php?f=12&t=7523&start=30
http://joesaward.wordpress.com/2010/06/ ... s-the-eye/
http://www.jamesallenonf1.com/2011/03/f ... nst-lotus/