I can tell you how that happened. Number one, you live in the rust belt. You eastern states are slow to learn sodium chloride does more harm than good, including polluting the environment. It does billions of dollars of damage every year, solely because people clean roads and won't learn to drive in winter.
In your case, getting in your vehicle in the winter with snow on your shoes, tracks in the salt. It has no where to go, and when it melts, it sits on the metal. A few car companies, especially Honda, had a brilliantly stupid idea long ago, to put the ECM on the floorboard on the passenger side. As a result, an older fuel injected Civic or Accord would come in on a wrecker, not running. Pull the carpet back, and the ECM and harness have all rotted away from the same affect.