The article states that libertarians, in at least two cases, voted for Libertarian Party candidates by margins large enough to ensure Democratic victory. This assumes that the Republican Party is the natural home of libertarians, and if the candidate in Montana had not got nearly 3% of the state vote, most of those votes would have gone to Burns, the Republican.
It is hard to imagine a committed Libertarian 'punishing' the Republicans by voting Democratic. Less so by voting Libertarian, though the outcome of either is close to the same. (Donkeys in Charge.)
It's not close to the same, it's exactly the same outcome.