Well, of course, it can't. The pertinent question is do good bacteria and bad bacteria both like or dislike iodine, or do they react differently to it. They are different species, so they don't necessarily like the same things.
However, my experiement doesn't really claim anything about bad bacteria. I suppose the fact that I didn't properly pasturize the cream means that any bad bacteria that got into the cream after it was initially pasturized might have survived my heat treatment, but they either didn't survive the Iodine or the yogurt culture was enough stronger than them that it was able to compete more successfully. We don't really know which. All we know is that the good did survive, because they soured and thickened the cream. It could even be that they did so in spite of the iodine, and that if I had used 30 drops in a single cup, it would not have cultured. This is too expensive an experiment for me. Also, you could try not adding any culture at all, but just leaving the differently treated milk or cream on the counter, but then would you really want to taste test the result? Personally, I don't have a lab to check bacterial counts. I don't know how hard that would be to do.
What dosage are those cows getting anyway? And what kind of bacteria is represented in those low bacterial counts?