The summary isn't entirely accurate. The candidates were actually chosen at the state party conventions over the summer. Please remember that when you vote for President, you're not actually casting a vote for the presidential candidate of your choice, but instead for a slate of electors. Those electors were chosen by their respective parties long before the election date.
Thus, the candidates were nominated and officially listed. The candidates' names are simply short-hand for a slate of electors--the people you're really voting for.
For a party that claims to be about enforcing the Constitution, the Libertarians seem to know very little about the document.