All human action involves choice and exchange. Even under the conditions of significant government intervention, individuals are still making choices - choosing what food to buy, what clothes to wear, what furniture looks nice, etc.
This means small elements of the free market - voluntary exchange driven by subjective preferences - are persisting despite restrictions. The conditions and incentives may be distorted by regulations, price controls, subsidies etc - but the exchange itself remains free on an individual level.
So everyday market decisions represent an instance of the free market in action - the aggregation of subjective preferences through voluntary exchange. This illustrates that even in an economy with significant government interference, free market forces continue to operate at a micro level.