Permaculture can be very productive if you're looking to raise a wide variety of food and medicinal plants in a small area. It's also great for reclaiming areas of poor soil for food production--I've seen a lot of sterile urban and suburban lawns transformed that way. It requires little to no inputs as far as machinery or chemicals; it's really about building up organic matter in the soil and working with microbes, fungi, earthworms, etc to create soil that is a thriving ecosystem unto itself, and in which plants can flourish.
But you have to know what the fuck you're doing. And these kids may have watched a couple of videos, but they don't know what the fuck they're doing. There's no straw mulch over...whatever that bagged soil is. The cardboard underneath it will smother the grass, and both will gradually rot, which should allow the roots of new plants to grow down through it into the soil--but the soil underneath is no doubt poor and packed-down, after decades of being a lawn in a public park. If anybody brought so much as a turning fork along to lift, loosen, and aerate the soil beneath the lawn before dumping cardboard and bagged soil on top of it, I would be shocked.
One other thing about permaculture--it takes time. You're not so much growing plants at first as you are growing soil, and a healthy microbiota. It takes at least a couple of years, and lots of compost, to get it there. You can still grow food in a brand-new bed, but you won't get a lot out of it, and the plants are more valuable for what they're doing at root level, underneath the soil, than above it.
