Decomposition Rate of A Body In A Wet Environment
It depends on the temperature of the environment as well. In the heat of summer and in a watery environment, I can verify through unfortunate personal reference that stuff can decompose very quickly. I honestly didn't look at the image, but judging by your description it can't have been there a year. There would be nothing left. Hungry bacteria and decomposers would have left nothing but bones by then. I would say your guess is more on target.