This seems as if the speaker/writer has lost an election through a democratic voting process he/she assumed they would win. The fact that they have lost seems to surprise them and the only logical assumption they can make is that somebody was not present to vote for them. Therefore they 'missed a vote'.
"Missing a vote" -
Imagine that only five people could vote, of these five, three had promised the speaker/writer that they would vote for him/her. This would mean he/she would win given the majority of votes. If one of those three didn't submit their vote, then he (The voter) has missed the opportunity to vote and the candidate has missed a vote that otherwise would have gone to his/her tally (tally = sum of votes).
Of course, the more likely situation is that the voters simply changed their preferences and voted for somebody else.
Hope that helps.