Who's to say that they're only gardening on this single plot of land? Why not plant a food forest in your front and back yard, and coordinate with your neighbors to have the whole neighborhood build a food coop?
Also, how do you get "feed your neighbor every single calorie they will ever need" out of this meme? You're literally just loading a whole bunch of extra baggage onto a simple point that we should be growing and sharing food for our community. There's no reason to make perfect the enemy of good.