I don't think this is entirely true. Polymarket is extremely transparent on user accounts and markets so you can see who is betting what, their other bets, and so on. The article mentions that other users fingered him for insider trading. That itself opens up an opportunity for profit, by simply following the trades on what he seems to be an insider on. It'd be like if you could see in real time what Nancy Pelosi was investing it - shadow her trades and make big bucks with the soon to be announced market shifting government deal/regulation/etc.

The markets also open up the door for hedging, arbitration and other sorts of opportunities where you don't necessarily even care what the result is.