Theoretically, the only way to make money on an efficient market is to have information others don't have. Manufacturing it would one (very desperate) way.

I agree that this would be too difficult to pull off (one worker spilling the beans would be enough).

But "can make money on the market" mean "might make money" not "will make money". Worth keeping in mind that hedge don't just get stream of money from the market just for being hedge funds. You need to get good information somehow.