You misunderstand. Money doesn't flow into or out of markets on net. Every time a share is sold for $X, a share is bought for $X - they are two sides of the same transaction.
The chart in the original article is of Annual Equity Fund flows, which are net values _considering both sides since it includes negative values_ -- a measurement of this supposedly nonexistant flow. While money remains constant from a trade, the stock of equity (in both senses of the term "stock") changes.