I think as humans we are really bad at intuition about probabilities, and it being an election only makes it much worse. I don't think anyone is consciously conflating these with poll numbers but percentages of voters are the numbers we see a lot more than prediction markets, and 80% is idunno an 80% chance of getting between 50% and 54% of the vote or something.
Every single factor was pointing towards Bolsonaro, Polymarket was just consistent with that.
He unexpectedly won the first round of the election. His lead was expected to grow since he'd likely get most of the votes of the other candidates. 17 out of 18 polls favored Bolsonaro. Market movements indicated a strong expectation of him winning. The Brazilian Real futures are already down 10% in the last couple hours.
But that's how democracy works, I think this election will be studied many times in the future.
Brutal.
If you bet on 20% chances and they happen 30% of the time you make money. The payoffs are such that you win by being a better predictor than the market. I'm fine criticizing it as a gambling blight (not to mention a corruption payoff) but it is also a prediction market.