Read this carefully because Stratchan is attacking property rights. He is saying that only the state should decide to whom an Australian should sell his property. If a Japanese investor wants to buy an Australian farm, Stratchan argues that the Australian has no right to sell without permission of some politician or bureaucrat, regardless of how much keen the farmer is to deal. Markets are not systems, they are processes. This fact is vital to any genuine understanding of how markets operate.
Numbers are totally irrelevant.
What matters is not the numbers of producers but whether artificial barriers have been erected to hinder entry into the market. Of course they are not free markets because the state has deliberately obstructed entry by potential competitors. Something that dreaded economic rationalists have protested, not that Stratchan bothered to mention that fact. Oligopoly is a market only if you stretch the meaning of 'market'. And THAT is the form of most markets in Australia today.