In this election, the spoiler candidate was the Republican. If the Republican hadn't run, the Democrat would've beaten the Progressive, and the majority of voters would've preferred that outcome (including the majority of Republican voters who assumedly thought that their honest rankings would be properly reflected in the election result).
It's a confusing example because we're used to spoiler candidates coming from third parties, but the politics in Vermont are a little bit unusual.
I don't see the problem?
The third party won. That's not a spoiler. And several of the criticisms listed on that page are really dumb.
Edit: Okay, so someone else would have won using ranked pairs... that's a different problem from "a spoiler" though.