Wolfe said that he felt stuck, so he chose a Damon Runyon story at random to bounce off of. The random story he chose was one he didn't like and apparently didn't feel inspired by, but he stuck it out, and by the end he had removed most of the similarity to that story. I think it's plausible that by the time he got to what is now the end of the story, he was sick of it and just ready for it to end. So he blew it up. But how would a woman have sex while wearing an explosive vest and the man doesn't notice? The hell with it. He went back and made the other incendiary explosive vests invisible too. And I can imagine him thinking, 'A few readers are going to be bothered about the explosive vests. They read THIS story and they're focusing on THAT? Screw them.' Of course I have no real evidence what he was thinking. This just seems kind of plausible to me.