Walled gardens have emerged from within the distributed network of the Internet. These pockets of the Internet, such as Apple App store, Facebook, Amazon, are controlled by centralised, hierarchical power structures. They differ from the the egalitarian nature of the open internet where every node acts as an entry point to the network and every node has the ability to broadcast to the entire network.
This podcast employs the concept of the walled garden, as if it where a literal garden with flowers, soil etc. The podcast aims to bring in to question whether walled gardens are actually beneficial, via a satirical gardening show which attempts to explain how the lord of the manor (the garden owner) benefits from a walled garden situation, as opposed to a free and open system (the national park example).
With regards to the concept of feudalism on the Internet, the owner of the walled garden is the feudal lord and guests in his walled garden are the medieval peasants.