That looks like the small/Kindle end of the cable. So most likely it somehow ended up in a small pool of water, or some really big wet bug tried to crawl into it.
Bingo! Last week I knocked a glass of cranberry juice over on my nightstand, some of it spilled down into the area between the bed and the nightstand where the Kindle-end of the cable was lying.
I see no evidence of damage with the charger, it charges the Kindle and shuts off when the Kindle is fully charged.
I had forgotten about the spill until you reminded me.
tanstaafl.