DEW is indeed a good theory.
I think a "tuned" nuke is more likely. Caused resonance - like pumping a swing, incredibly fast.
You can see the EM Pulse (or its effect).
It affected radio and video for a moment.
Blew out tires, etc.
Think of a massive, temporary Electromagnetic Pulse, like what would drive a speaker coil. Driven so fast it heats up and 'dustifies' - molecular dissociation.
DEW isn't the only way to achieve dustification.
Look into what Tesla did with a building, using his Electro-Mechanical resonator - almost shook the building down.
This was on another "octave" - higher frequency, greater energy, shorter 'pulse'.
Caused the Hutchison Effect in beams (the beams bent into a pretzel, the ones that didn't quite dissociate, but had 'jellification' - turning to jelly, then hardening (resolidifying) again quickly as they cooled.
All will fit when viewed through the proper lens.