If you haven't opened your bottle, odds are pretty good that it wasn't iodine tablets.

"Everything" had corroded? Tell us more- what is everything? Aluminum? Steel? Stainless steel? Copper? Ferro rods? Plastics? If was iodine, it probably would have pitted some of your plastics and left a distinctive smell, and any cloth items that were pale and near the bottle may be stained. Iodine is pretty agressive, it chews up everything but glass, teflon and enamel.

I'm more inclined to think it was just good old fashioned water. Something wet was in there, or you got rain in it, something like that. Moisture will kill a ferro rod if you give it time.