The article cites income increase but doesn't talk about the necessary factors even if you're only talking numbers:

1) real inflation (ie, cost of living has skyrocketed due to rent/medical) outweighs any income increases.

2) overall wealth was not accounted for - in fact many Americans are living paycheck to paycheck, probably far more than at any corresponding postwar period in the US.

In short "prosperity" != income. Ignoring things like cost of living and the high possibility of surprise bankruptcy due to medical emergencies lead to a very inaccurate picture.