I’m not sure being under the federal poverty line (or 2x cutoff as this article used) means the same thing at retirement age.
My mother, for example, has a monthly post-tax income of $1,400 or just under $17,000 per year. She must be poor right?
However, she owns her home outright. So her total reoccurring monthly expenses are around $1,200. That includes property tax, condo fees, health insurance premium, food and gas for the car. She has a very comfortable life. She would certainly not call herself poor.
She can basically live off her pension without touching the equity in her home or the savings she has (unless it’s for something important like travel).
A lot of people in retirement are no longer relying on income, instead they are taking money out of savings as well. Not sure if this paper accounted for that.