Simply put... Powerful photo.
"The photographer has denied deliberately attempting to manipulate the image, saying that he was trying to remove dust marks and that he made mistakes due to the bad lighting conditions he was working under," said Moira Whittle, the head of public relations for Reuters.
The only reason he did this was to sensationalize the scene and I think he's just blowing smoke with this excuse. You don't clean up dust by cloning smoke.