it shows the vulnerability of the system, and direct evidence that voter fraud is possible.. .it's relatively easy to get caught, too. And the impact of that individual voting twice is so infinitesimally small that any rational person considering voting twice would have to conclude it was apointless effort because the risk reward ratio was so high. Jail vs. a tiny infinitesimal increase in "your" candidate's tally in another state.
I would say it is an inside job and Bannon case is just on of the many others that gave not been discovered. The electoral system is very complex and very hard to hack, any attempt for double registration will be flagged by the system. But as they say the system is just as good as the people using it.
Trump has no real facts on voter fraud, only alternative ones, which is to say none. He's thin skinned enough to resent losing the popular vote, so his cronies have found a way to make him think that he really didn't, by convincing him there was large scale voter fraud. Worse, some 'top' Republicans are going along with this.
If a person so close to the campaign is registered in two states, and it was that easy to find out, imagine how many others are registered in multiple states that we don't know about. The campaigns could be sending hundreds or even thousands to go out and vote in multiple states to try and swing the election, and we wouldn't even know it given that each state is separate. I imagine it happens more than we would like to think.