I attempted this a couple times, the cache folder is not modified on my phone. I'm guessing the software indexes free space that has been recently assigned 'empty' status and tries to piece together the image or directory. I could be wrong, though.
This article seems link baity. It doesn't talk about the Snapchat servers not deleting photos, but the Snapchat app storing photos locally in a "hidden folder". It then advertises a $300-$500 service to remove the photos in the hidden folder.
Either way it's an issue. Now that it's known, how many minutes will it be before some high schooler retrieves sexts sent by their now-hated ex, and distributes them to all their classmates? I suspect the number is negative.
Nevermind, it appears that the photos are not as present as the original press release would have you believe: