The article is opinionated and sensationalist.

The fact remains that prediction markets and financial markets are not the same thing. Bets between people happened all the time, and you would wager based on information asymmetry, that is the whole point of it.

By making these markets public facing, you get access to this information asymmetry, whereas before it was behind doors, and these bets were already taking place, you just didn't know it, now you do.