The problem here, is that groceries are real. But stocks are not! Their price goes up and down based on the performance of the issuing organisation. CPI IS the real measure of inflation for ordinary people. It's a true measure of their purchasing power for the majority of their day-to-day purchases. What you are talking about applies only to the very rich.
Further down the article you talk about 'free money' being handed out to people whose incomes have been devastated by the pandemic. They are not going to go out and purchase stocks, as you assert. They need that 'free money' to purchase groceries. Without it most would be relying on food banks.