"The whole jug looked like it had been vacuum sealed: it was all shriveled and collapsed."

This sounds like a leak down low in the jug. I have put full, capped milk jugs near plants to give them a slow-drip watering, & they end up looking that same way.

I suspect this was just a bad jug that someone had dropped or punctured. I've stored water jugs in my garage fruit room (insulated) & never had it happen.

I think it was bad luck rather than poor planning. Before you toss the canned goods, open them & see if the rust has gone to the inside. I understand that if it hasn't, it is okay to eat. But I wouldn't use it for continued storage.

Sue