Allegations that Critz was campaigning in polling booths on the date of the election, as well as strategically mailing duplicate ballots, are indicative of his character, but do not explain alone how he outperformed the polls (generally conducted by partisan Democrats) suggesting he would win by a small margin. Democrats were certainly preparing for a loss, noting that the demographics of the district no longer favored the ideology of the party and the loyalty that many of its inhabitants had to the party had radically diminished in the last three presidential elections.
I'm not clear what you mean by "strategically mailing duplicate ballots." It has become common for the parties to mail out absentee ballot applications.