I did some google search and found this statement on the Nikon D3 brochure found on page 15 of the pdf file on the upper left hand corner.
" Countermeasures against dust, moisture and
electromagnetic interference The D3 goes the extra mile to protect against invasive moisture, dust and
even electromagnetic interference. A comprehensive series of O-rings and other specialized seals, combined with additional Nikon engineering, keeps you shooting when lesser cameras would fail."
http://imaging.nikon.com/products/imaging/lineup/digitalcamera/slr/d3/index.htm
Would this statement justify why the guy placed the Nikon D3 inside the microwave?
I'm not sure if microwave radiation and EMI are similar with regards to frequency...Any electronics or electrical engineer my comment or shed some light.