You have to know where to go, what to buy, and what to cook.
I've been a vegan for a number of years now and I could live off $60/mo if I wanted to. The main point is convenience. If you don't want the effort of preparing food then it costs a lot more. Simple staples like lentals, rice, etc supplemented with vegetables is a crazy cheap way to eat.
In SF districts like the mission it's easy to get cheap fresh fruit and vegetables. A lot of it is supply and demand. If you shop at Safeway they have an expectation about your spending and price accordingly.
If you are trying save every penny shop where other people who have no money shop. That probably means neighborhoods you might avoid otherwise.
It's not a typo. In the post I mentioned Three Guys From brooklyn, here's a link to their weekly circular. http://3guysfrombrooklyn.tripod.com/id4.html, note that the price listed for fruit and vegetables in that circular are about the average prices for all their fruits and vegetables. Certainly things like packaged foods will be a little higher, but if you purchase mostly fruits, vegetables, tubas (the average price of a bag of 5lbs potatoes there is $1.99), etc, in addition to a few packaged foods such as orange juice, you can easily eat for less than $60 a month.
Is that a typo? $60/mo eating fruits and veggies? I live in SF and I have a hard time imagining doing that here, let along NYC...