Where did you get this information?

If you're only making ~ 20k a year with two people in the household for more than 6 months out of the year, you're considering below the level... And I'm pretty sure you still have to pay taxes. I know people that make less and still pay taxes. If you flip burgers 3 days a week and make 165 each week it's probably because you already paid $50-100 in taxes.

People living below the poverty level are often, but not always, eligible for tax deductions and credits... The specific income requirements for tax breaks are not tied to the same income thresholds as the poverty guidelines.