The Actual Forbes article from which the Yahoo article is derived is based mostly on most affordable places to retire ... according to Forbes. Fargo, ND qualifies with a population of about 91K has an average income of $35K and housing value of about $68K. --- But, the inference that great numbers of people are flocking to Fargo ND to retire, ... isn't really supported.
The Best Retirement Places - William P. Barrett - Informer - Forbes
There are a number of other respected lists available on the web that list the top 100-200+ places where people are actually retiring --- most of which, naturally, focus on the sunbelt.