Worth noting that, had this been an international flight (it wasn’t), there could be legitimate need to verify that both adults were the child’s parents. I learned this the hard way taking a daughter across the border to Canada.
https://de.usembassy.gov/visas/travel-tourism/travelers-faqs/children-traveling-with-one-parent-or-with-someone-who-is-not-a-parent-or-legal-guardian/
