As I read it, the microwaves heat up the shale enough to make the petroleum separate out and liquefy.
Future Of Fracking Could Be Beaming Up Oil With Microwaves
From the article:
"Microwave fracking would zap shale formations with a beam as powerful as 500 household microwave ovens to release the valuable oil or gas. Experts estimate the first microwave fracking systems could be deployed in the field by 2017 and start producing oil by the end of that year."
It is the “... condense and boil ...” language that makes no sense.