Man, your debating skills are impeccable.
Read the rest of the thread.
How is it not possible?
Assume the following: if he's growing food, he has enough water to do so, and as much land as he requires, because everyone is dead. He eats eight potatoes a day. He requires 2,920 potatoes a year. Potatoes take four months to grow (May, June, July, August). Each potato plant yields an average of a dozen potatoes, size varying on time of harvest.
He needs to plant 243 potato plants (2,920/12). Let's say you give each potato plant a very generous three feet of clearance. He has to plough 729 feet of soil. Let's say with the help of an animal or animals, he can plough and seed 120 feet of soil per day (or plant 40 plants).
He should be able to plant all the plants he needs in about a week. He has 51 other weeks in the entire year to supplement his diet by hunting, planting other crops, and scavenging, not to mention attempt reconstruction and whatnot.
1 week out of 52. That's leaving a significant margin for error. Sure, drought, famine and whatnot will take its toll on people. Nobody said it would be easy.