The parent post is not talking about managers, they receive a salary and are taxed at regular income rates. It's taking about shareholders. Someone who makes money by owning a stock should be taxed more aggressively that someone earning a salary, IMO.
But a company director is usually both? And often forgoes salary for ownership.
The parent post is not saying that some forms of shareholding do not earn, but they are excluding any form of owning a bricklaying firm is definitively not earning. So any arrangement that involves owning a bricklaying firm is within scope. Sole Trader or Partnership for instance.