I think the math in this assumes everything is being sown directly into the ground, which for a lot of things is the least space-efficient option.

You can hang-grow tomato plants, vertical garden stuff that doesn’t need much soil, and build potato towers to reduce the footprint (25 sqft turns into 5 sqft pretty easily), and leaf veg/herbs grow very well in window planter boxes or pots (with or without supplemental light). You can also grow mushrooms for protein and those hardly take up any space, and can produce very prolifically (and are mostly grown inside anyway).

Lots of options to reduce the actual space needed to grow stuff for self-sustaining food.

Although I’m honestly an advocate for either growing in soilless (cococoir) or hydroponic, if you have the space to have those inside. A single tomato plant is enough for most people, and a couple bell pepper or other self-pollinating plants (easier than pollinating them yourself with a paint brush). Year round fresh foods are so worth it, and a lot easier than canning everything.

I’m sorry but this article is ridiculous.

-Proteins. If you’re going to survive on a garden, you won’t be eating meat.
…
Growing lima beans on poles will require about six square feet of garden per person.

Like for a meal or two. Not for a year. Not to survive on.

I’ve grown all kinds of things. Worked at community farms. Been hired to grow fruits and veg for other people at their homes as a side thing. Pruned and managed small fruit tree orchards.

A 2 foot by 3 foot patch of beans takes 60 to 90 days to grow, and that is not going to feed anyone more than once or twice. Whoever wrote this does not know what they are talking about. Like at all.