The article mentions getting protein via the forms of bean and rice, eggs, whey protein powder. No wonder you/the author can stay under $2/meal :)
As for myself, I still like to enjoy meat like beef, chicken, pork. Meat is typically the most expensive part of grocery. Even enjoying good quality meat like the ones above, one can easily stay under $5/meal!
You don't have to stay under $2 for every meal as long they average out to that value. It's possible to eat high quality meat while hitting that number - you just can't eat it for every meal.
As for myself, I still like to enjoy meat like beef, chicken, pork. Meat is typically the most expensive part of grocery. Even enjoying good quality meat like the ones above, one can easily stay under $5/meal!