From the article, he was convinced McDaniels was a racist and thus he used an 'ends justify the means' rationale to break the law. The old 'greater good' play. Afterward, he learned he was duped as well as stiffed. Further, he had voted Republican before so there was likely feelings of guilt.
Besides, confession is good for the soul.
I listened to an audio of an interview with him. THe “racist” charge was his excuse for doing what he did. He would have kept his mouth shut had he received the money he thought he was owed from the Cochran campaign. He was trying to get money from the McDaniels’ campaign. If he’s legit, he is monumentally stupid because he’s admitted to paying people for their votes.