These kind of findings are pretty common (though usually less colorful). The idea is that it’s very, very difficult for anyone — from the smallest individual investor to the biggest mutual fund manager — to beat the market average. In the case of this story, they’re having a cat stand in for the market, to make the professional stock pickers look more ridiculous.
It’s true that some stock pickers do better than average and some do worse. But of course this is what would happen if everybody were picking randomly.
Once you take into account things like management fees and transaction costs, actively managed mutual funds that try to beat the market typically end up doing worse than index funds that passively track the overall stock market.