paying taxes and social security taxes

My fiancé is on social security disability and has a side gig. The side gig is considered as self-employment (DoorDash). When we did his taxes on TurboTax it said he had to pay $257.00 to the federal government. It then asked if he wanted extension to pay the social security admiration back their share of taxes. So we said yes. It took the amount that he owed to the federal government and it applied to the social security admiration. Now it says he owes nothing to the federal government. Could this be true?