South Park: My favorite lunch spot and its garden truck

As many of you know, I spend most of my lunches in South Park. It's a wonderful spot, not only for it being a green enclave in cement covered SOMA but for the subtle characters that populate the parks benches every day. In any event, there is pickup truck parked at almost all times on the north side of South Park, right in front of South Park Cafe, whose back section is always filled with plants: flowering, leafy, and fruiting (tomatoes!). I'm not really sure why this truck is there and filled with greenery; the plants don't appear for sale and there is no marking indicating how pedestrians should treat this garden in this public space. I am going to guess, however, that the placement of these potted plants could be using the possibly unused space of the back of a pickup to produce food as well as reducing the trucks CO2 emissions. How sweet. Is this possibly some green art installation/victory garden of sorts? Or is it simply intended to add a view to South Park's already pretty park setting?

I tried to do some research on the internet and found nothing on the truck, but did find a cool historical photograph of my favorite park. In any event, does anyone know the true role of this mini truck garden? Thanks.