I suspect that the problem you had with your batch of "field expedient" saline solution were caused by a spec of dirt that got into the mix. I know that dirt under a contact can hurt like Holy Blazes. I doubt that it was the iodine that caused your problem.
No, it wasn't a speck of dirt. I know what that feels like. My chemist boyfriend, who was with me at the time, was convinced it was the iodized salt. But he was a jerk, so I'm happy to take your word for it.
I have, however, successfully used tap water in a pinch (traveling, no solution, stores closed, no glasses or extra pair of contacts).