2x teleconverter for macro?

I was reading a thread on the Nikon FX forum where a poster, Stany Buyle, showed some amazingly clear macro shots of a dragonfly's eyes where he said he used a TC20E III.

I've read all sorts of lens combos for macro: regular macro lenses, extenders, screw-on adapters and lens-reversing adapters. That was the first time I'd read about using a teleconverter. Just wondering why?