My initial thought was that someone at the Social Security field office must have been in cahoots with the scammers but one fact kept drawing my attention -- the number the man was given to call was only one digit different from the real number. If you had someone on the inside who was funneling calls to you, why would you go to the trouble of obtaining a phone number so similar to the real one?
Let me posit a theory for what happened. Nobody at Social Security was in cahoots with the scammers. The number on the sheet was a simple typo. What had happened was that scammers had obtained as many telephone numbers as they could that were one digit different from the real number. Probably they did this for many offices. They could then expect a steady stream of misdials from people who thought they were talking with a Social Security office. By chance, the sheet handed out by Social Security funneled more calls to them but it wasn't part of their scheme. Actually, the typo may end up exposing their scheme.
That's my theory. Have you got a better one?